Leetcode-Archive

Collection of solutions to the 600+ Leetcode questions I've solved over the past ~2 years

Table Of Contents

• 2020

  • July (19 questions)
  • June (28 questions)
  • May (41 questions)
  • April (28 questions)
  • March (23 questions)
  • February (29 questions)
  • January (17 questions)

• 2019

  • December (11 questions)
  • November (6 questions)
  • October (9 questions)
  • September (32 questions)
  • August (38 questions)
  • July (27 questions)
  • June (26 questions)
  • May (38 questions)
  • April (37 questions)
  • March (52 questions)
  • February (23 questions)
  • January (23 questions)

• 2018

  • December (2 questions)
  • November (11 questions)
  • October (8 questions)
  • September (36 questions)
  • August (7 questions)
  • July (11 questions)
  • June (3 questions)

2020

July

Find Root of N-Ary Tree - #1506 | Difficulty: Medium | View Code

Design a File Sharing System - #1500 | Difficulty: Medium | View Code

Number of Substrings With Only 1s - #1513 | Difficulty: Medium | View Code

Number of Good Pairs - #1512 | Difficulty: Easy | View Code

Last Moment Before All Ants Fall Out of a Plank - #1503 | Difficulty: Medium | View Code

Can Make Arithmetic Progression From Sequence - #1502 | Difficulty: Easy | View Code

Number of Subsequences That Satisfy the Given Sum Condition - #1498 | Difficulty: Medium | View Code

Path Crossing - #1496 | Difficulty: Easy | View Code

Minimum Difference Between Largest and Smallest Value in Three Moves - #1509 | Difficulty: Medium | View Code

Range Sum of Sorted Subarray Sums - #1508 | Difficulty: Medium | View Code

Maximum 69 Number - #1323 | Difficulty: Easy | View Code

Divide Array in Sets of K Consecutive Numbers - #1296 | Difficulty: Medium | View Code

Reformat Date - #1507 | Difficulty: Easy | View Code

Remove Covered Intervals - #1288 | Difficulty: Medium | View Code

Serialize and Deserialize N-ary Tree - #428 | Difficulty: Hard | View Code

Longest Repeating Character Replacement - #424 | Difficulty: Medium | View Code

Nested List Weight Sum II - #364 | Difficulty: Medium | View Code

Best Time to Buy and Sell Stock II - #122 | Difficulty: Easy | View Code

June

Clone N-ary Tree - #1490 | Difficulty: Medium | View Code

Clone Binary Tree With Random Pointer - #1485 | Difficulty: Medium | View Code

Check If Array Pairs Are Divisible by k - #1497 | Difficulty: Medium | View Code

Delete N Nodes After M Nodes of a Linked List - #1474 | Difficulty: Easy | View Code

XOR Operation in an Array - #1486 | Difficulty: Easy | View Code

Find All The Lonely Nodes - #1469 | Difficulty: Easy | View Code

Running Sum of 1d Array - #1480 | Difficulty: Easy | View Code

The kth Factor of n - #1492 | Difficulty: Medium | View Code

Average Salary Excluding the Minimum and Maximum Salary - #1491 | Difficulty: Easy | View Code

Design Browser History - #1472 | Difficulty: Medium | View Code

Shuffle the Array - #1470 | Difficulty: Easy | View Code

Maximum Product of Two Elements in an Array - #1464 | Difficulty: Easy | View Code

Subrectangle Queries - #1476 | Difficulty: Medium | View Code

Final Prices With a Special Discount in a Shop - #1475 | Difficulty: Easy | View Code

Pseudo-Palindromic Paths in a Binary Tree - #1457 | Difficulty: Medium | View Code

Check If a String Contains All Binary Codes of Size K - #1461 | Difficulty: Medium | View Code

Make Two Arrays Equal by Reversing Sub-arrays - #1460 | Difficulty: Easy | View Code

Simplified Fractions - #1447 | Difficulty: Medium | View Code

Maximum Number of Occurrences of a Substring - #1297 | Difficulty: Medium | View Code

Search Suggestions System - #1268 | Difficulty: Medium | View Code

Synonymous Sentences - #1258 | Difficulty: Medium | View Code

Camelcase Matching - #1023 | Difficulty: Medium | View Code

Maximum Frequency Stack - #895 | Difficulty: Hard | View Code

Find And Replace in String - #833 | Difficulty: Medium | View Code

Shortest Word Distance - #243 | Difficulty: Easy | View Code

Read N Characters Given Read4 - #157 | Difficulty: Easy | View Code

Longest Consecutive Sequence - #128 | Difficulty: Hard | View Code

May

Maximum Number of Vowels in a Substring of Given Length - #1456 | Difficulty: Medium | View Code

Check If a Word Occurs As a Prefix of Any Word in a Sentence - #1455 | Difficulty: Easy | View Code

People Whose List of Favorite Companies Is Not a Subset of Another List - #1452 | Difficulty: Medium | View Code

Rearrange Words in a Sentence - #1451 | Difficulty: Medium | View Code

Number of Students Doing Homework at a Given Time - #1450 | Difficulty: Easy | View Code

Build an Array With Stack Operations - #1441 | Difficulty: Easy | View Code

Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit - #1438 | Difficulty: Medium | View Code

Destination City - #1436 | Difficulty: Easy | View Code

Count Good Nodes in Binary Tree - #1448 | Difficulty: Medium | View Code

Consecutive Characters - #1446 | Difficulty: Easy | View Code

Kids With the Greatest Number of Candies - #1431 | Difficulty: Easy | View Code

Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary Tree - #1430 | Difficulty: Medium | View Code

Counting Elements - #1426 | Difficulty: Easy | View Code

Perform String Shifts - #1427 | Difficulty: Easy | View Code

Distance Between Bus Stops - #1184 | Difficulty: Easy | View Code

Longest Repeating Substring - #1062 | Difficulty: Medium | View Code

Delete Columns to Make Sorted - #944 | Difficulty: Easy | View Code

Fair Candy Swap - #888 | Difficulty: Easy | View Code

Masking Personal Information - #831 | Difficulty: Medium | View Code

Search in a Sorted Array of Unknown Size - #702 | Difficulty: Medium | View Code

Convert Binary Search Tree to Sorted Doubly Linked List - #426 | Difficulty: Medium | View Code

Binary Number with Alternating Bits - #693 | Difficulty: Easy | View Code

Next Closest Time - #681 | Difficulty: Medium | View Code

Base 7 - #504 | Difficulty: Easy | View Code

Binary Watch - #401 | Difficulty: Easy | View Code

Design Tic-Tac-Toe - #348 | Difficulty: Medium | View Code

Bulls and Cows - #299 | Difficulty: Easy | View Code

Flip Game - #293 | Difficulty: Easy | View Code

Group Shifted Strings - #249 | Difficulty: Medium | View Code

Lowest Common Ancestor of a Binary Search Tree - #235 | Difficulty: Easy | View Code

Course Schedule - #207 | Difficulty: Medium | View Code

Reverse Words in a String II - #186 | Difficulty: Medium | View Code

Two Sum III - Data structure design - #170 | Difficulty: Easy | View Code

Excel Sheet Column Title - #168 | Difficulty: Easy | View Code

Single Number - #136 | Difficulty: Easy | View Code

Clone Graph - #133 | Difficulty: Medium | View Code

Binary Tree Maximum Path Sum - #124 | Difficulty: Hard | View Code

Text Justification - #68 | Difficulty: Hard | View Code

Insert Interval - #57 | Difficulty: Hard | View Code

April

Diagonal Traverse II - #1424 | Difficulty: Medium | View Code

Maximum Score After Splitting a String - #1422 | Difficulty: Easy | View Code

Minimum Number of Frogs Croaking - #1419 | Difficulty: Medium | View Code

Reformat The String - #1417 | Difficulty: Easy | View Code

HTML Entity Parser - #1410 | Difficulty: Medium | View Code

String Matching in an Array - #1408 | Difficulty: Easy | View Code

Number of Steps to Reduce a Number in Binary Representation to One - #1404 | Difficulty: Medium | View Code

Minimum Subsequence in Non-Increasing Order - #1403 | Difficulty: Easy | View Code

The k-th Lexicographical String of All Happy Strings of Length n - #1415 | Difficulty: Medium | View Code

Minimum Value to Get Positive Step by Step Sum - #1413 | Difficulty: Easy | View Code

Count Number of Teams - #1395 | Difficulty: Medium | View Code

Longest Happy Prefix - #1392 | Difficulty: Hard | View Code

Count Largest Group - #1399 | Difficulty: Easy | View Code

Bulb Switcher III - #1375 | Difficulty: Medium | View Code

Number of Substrings Containing All Three Characters - #1358 | Difficulty: Medium | View Code

Remove Palindromic Subsequences - #1332 | Difficulty: Easy | View Code

Break a Palindrome - #1328 | Difficulty: Medium | View Code

Max Consecutive Ones III - #1004 | Difficulty: Medium | View Code

K-diff Pairs in an Array - #532 | Difficulty: Easy | View Code

Max Consecutive Ones II - #487 | Difficulty: Medium | View Code

Circular Array Loop - #457 | Difficulty: Medium | View Code

Valid Word Abbreviation - #408 | Difficulty: Easy | View Code

Sort Transformed Array - #360 | Difficulty: Medium | View Code

Longest Substring with At Most K Distinct Characters - #340 | Difficulty: Hard | View Code

Longest Substring with At Most Two Distinct Characters - #159 | Difficulty: Medium | View Code

Copy List with Random Pointer - #138 | Difficulty: Medium | View Code

Longest Valid Parentheses - #32 | Difficulty: Hard | View Code

March

Design Underground System - #1396 | Difficulty: Medium | View Code

Find Lucky Integer in an Array - #1394 | Difficulty: Easy | View Code

Create Target Array in the Given Order - #1389 | Difficulty: Easy | View Code

Find a Corresponding Node of a Binary Tree in a Clone of That Tree - #1379 | Difficulty: Medium | View Code

Design a Stack With Increment Operation - #1381 | Difficulty: Medium | View Code

Lucky Numbers in a Matrix - #1380 | Difficulty: Easy | View Code

Generate a String With Characters That Have Odd Counts - #1374 | Difficulty: Easy | View Code

Sort Integers by The Power Value - #1387 | Difficulty: Medium | View Code

Find the Distance Value Between Two Arrays - #1385 | Difficulty: Easy | View Code

Linked List in Binary Tree - #1367 | Difficulty: Medium | View Code

How Many Numbers Are Smaller Than the Current Number - #1365 | Difficulty: Easy | View Code

Find the Longest Substring Containing Vowels in Even Counts - #1371 | Difficulty: Medium | View Code

Increasing Decreasing String - #1370 | Difficulty: Easy | View Code

Delete Leaves With a Given Value - #1325 | Difficulty: Medium | View Code

Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold - #1343 | Difficulty: Medium | View Code

Find the Smallest Divisor Given a Threshold - #1283 | Difficulty: Medium | View Code

Number of Burgers with No Waste of Ingredients - #1276 | Difficulty: Medium | View Code

Koko Eating Bananas - #875 | Difficulty: Medium | View Code

Count of Smaller Numbers After Self - #315 | Difficulty: Hard | View Code

Minimum Size Subarray Sum - #209 | Difficulty: Medium | View Code

Valid Number - #65 | Difficulty: Hard | View Code

Count and Say - #38 | Difficulty: Easy | View Code

February

Product of the Last K Numbers - #1352 | Difficulty: Medium | View Code

Count Negative Numbers in a Sorted Matrix - #1351 | Difficulty: Easy | View Code

Minimum Number of Steps to Make Two Strings Anagram - #1347 | Difficulty: Medium | View Code

Check If N and Its Double Exist - #1346 | Difficulty: Easy | View Code

Maximum Product of Splitted Binary Tree - #1339 | Difficulty: Medium | View Code

Reduce Array Size to The Half - #1338 | Difficulty: Medium | View Code

The K Weakest Rows in a Matrix - #1337 | Difficulty: Easy | View Code

Apply Discount Every n Orders - #1357 | Difficulty: Medium | View Code

Sort Integers by The Number of 1 Bits - #1356 | Difficulty: Easy | View Code

Filter Restaurants by Vegan-Friendly, Price and Distance - #1333 | Difficulty: Medium | View Code

Print Words Vertically - #1324 | Difficulty: Medium | View Code

Angle Between Hands of a Clock - #1344 | Difficulty: Medium | View Code

Number of Steps to Reduce a Number to Zero - #1342 | Difficulty: Easy | View Code

XOR Queries of a Subarray - #1310 | Difficulty: Medium | View Code

Number of Days Between Two Dates - #1360 | Difficulty: Easy | View Code

Rank Transform of an Array - #1331 | Difficulty: Easy | View Code

Iterator for Combination - #1286 | Difficulty: Medium | View Code

Smallest String Starting From Leaf - #988 | Difficulty: Medium | View Code

Diameter of Binary Tree - #543 | Difficulty: Easy | View Code

Zigzag Iterator - #281 | Difficulty: Medium | View Code

Closest Binary Search Tree Value II - #272 | Difficulty: Hard | View Code

Closest Binary Search Tree Value - #270 | Difficulty: Easy | View Code

Basic Calculator II - #227 | Difficulty: Medium | View Code

Path Sum II - #113 | Difficulty: Medium | View Code

Convert Sorted List to Binary Search Tree - #109 | Difficulty: Medium | View Code

Convert Sorted Array to Binary Search Tree - #108 | Difficulty: Easy | View Code

Jump Game - #55 | Difficulty: Medium | View Code

Combination Sum - #39 | Difficulty: Medium | View Code

January

Convert Integer to the Sum of Two No-Zero Integers - #1317 | Difficulty: Easy | View Code

Decrypt String from Alphabet to Integer Mapping - #1309 | Difficulty: Easy | View Code

Jump Game III - #1306 | Difficulty: Medium | View Code

Group the People Given the Group Size They Belong To - #1282 | Difficulty: Medium | View Code

Find Winner on a Tic Tac Toe Game - #1275 | Difficulty: Easy | View Code

Shift 2D Grid - #1260 | Difficulty: Easy | View Code

Sum of Nodes with Even-Valued Grandparent - #1315 | Difficulty: Medium | View Code

Decompress Run-Length Encoded List - #1313 | Difficulty: Easy | View Code

Replace Elements with Greatest Element on Right Side - #1299 | Difficulty: Easy | View Code

Fixed Point - #1064 | Difficulty: Easy | View Code

Lexicographically Smallest Equivalent String - #1061 | Difficulty: Medium | View Code

Invert Binary Tree - #226 | Difficulty: Easy | View Code

Sum Root to Leaf Numbers - #129 | Difficulty: Medium | View Code

Permutations II - #47 | Difficulty: Medium | View Code

Roman to Integer - #13 | Difficulty: Easy | View Code

Longest Substring Without Repeating Characters - #3 | Difficulty: Medium | View Code

2019

December

All Elements in Two Binary Search Trees - #1305 | Difficulty: Medium | View Code

Find N Unique Integers Sum up to Zero - #1304 | Difficulty: Easy | View Code

Find Numbers with Even Number of Digits - #1295 | Difficulty: Easy | View Code

Convert Binary Number in a Linked List to Integer - #1290 | Difficulty: Easy | View Code

Subtract the Product and Sum of Digits of an Integer - #1281 | Difficulty: Easy | View Code

Count Square Submatrices with All Ones - #1277 | Difficulty: Medium | View Code

Minimum Time Visiting All Points - #1266 | Difficulty: Easy | View Code

Deepest Leaves Sum - #1302 | Difficulty: Medium | View Code

Element Appearing More Than 25% In Sorted Array - #1287 | Difficulty: Easy | View Code

Sequential Digits - #1291 | Difficulty: Medium | View Code

Hexspeak - #1271 | Difficulty: Easy | View Code

November

Print Immutable Linked List in Reverse - #1265 | Difficulty: Medium | View Code

Find Elements in a Contaminated Binary Tree - #1261 | Difficulty: Medium | View Code

Cells with Odd Values in a Matrix - #1252 | Difficulty: Easy | View Code

Web Crawler Multithreaded - #1242 | Difficulty: Medium | View Code

Design A Leaderboard - #1244 | Difficulty: Medium | View Code

Array Transformation - #1243 | Difficulty: Easy | View Code

October

Remove Sub-Folders from the Filesystem - #1233 | Difficulty: Medium | View Code

Check If It Is a Straight Line - #1232 | Difficulty: Easy | View Code

Split a String in Balanced Strings - #1221 | Difficulty: Easy | View Code

Day of the Week - #1185 | Difficulty: Easy | View Code

Web Crawler - #1236 | Difficulty: Medium | View Code

Missing Number In Arithmetic Progression - #1228 | Difficulty: Easy | View Code

Two Sum BSTs - #1214 | Difficulty: Medium | View Code

Intersection of Three Sorted Arrays - #1213 | Difficulty: Easy | View Code

Construct String from Binary Tree - #606 | Difficulty: Easy | View Code

September

Unique Number of Occurrences - #1207 | Difficulty: Easy | View Code

Minimum Absolute Difference - #1200 | Difficulty: Easy | View Code

Reverse Substrings Between Each Pair of Parentheses - #1190 | Difficulty: Medium | View Code

Maximum Number of Balloons - #1189 | Difficulty: Easy | View Code

Diet Plan Performance - #1176 | Difficulty: Easy | View Code

Compare Strings by Frequency of the Smallest Character - #1170 | Difficulty: Easy | View Code

Find Smallest Common Element in All Rows - #1198 | Difficulty: Medium | View Code

How Many Apples Can You Put into the Basket - #1196 | Difficulty: Easy | View Code

Count Substrings with Only One Distinct Letter - #1180 | Difficulty: Easy | View Code

Single-Row Keyboard - #1165 | Difficulty: Easy | View Code

Missing Element in Sorted Array - #1060 | Difficulty: Medium | View Code

Asteroid Collision - #735 | Difficulty: Medium | View Code

Maximum Distance in Arrays - #624 | Difficulty: Easy | View Code

Can Place Flowers - #605 | Difficulty: Easy | View Code

Shortest Unsorted Continuous Subarray - #581 | Difficulty: Easy | View Code

Subtree of Another Tree - #572 | Difficulty: Easy | View Code

Island Perimeter - #463 | Difficulty: Easy | View Code

Binary Tree Vertical Order Traversal - #314 | Difficulty: Medium | View Code

Binary Tree Longest Consecutive Sequence - #298 | Difficulty: Medium | View Code

Alien Dictionary - #269 | Difficulty: Hard | View Code

Palindrome Permutation - #266 | Difficulty: Easy | View Code

Binary Tree Paths - #257 | Difficulty: Easy | View Code

Flatten 2D Vector - #251 | Difficulty: Medium | View Code

Count Univalue Subtrees - #250 | Difficulty: Medium | View Code

Course Schedule II - #210 | Difficulty: Medium | View Code

Factorial Trailing Zeroes - #172 | Difficulty: Easy | View Code

Compare Version Numbers - #165 | Difficulty: Medium | View Code

Missing Ranges - #163 | Difficulty: Medium | View Code

Insertion Sort List - #147 | Difficulty: Medium | View Code

Generate Parentheses - #22 | Difficulty: Medium | View Code

Letter Combinations of a Phone Number - #17 | Difficulty: Medium | View Code

August

Day of the Year - #1154 | Difficulty: Easy | View Code

Longest Common Subsequence - #1143 | Difficulty: Medium | View Code

Snapshot Array - #1146 | Difficulty: Medium | View Code

N-th Tribonacci Number - #1137 | Difficulty: Easy | View Code

Maximum Level Sum of a Binary Tree - #1161 | Difficulty: Medium | View Code

Find Words That Can Be Formed by Characters - #1160 | Difficulty: Easy | View Code

Check If a Number Is Majority Element in a Sorted Array - #1150 | Difficulty: Easy | View Code

Largest Unique Number - #1133 | Difficulty: Easy | View Code

Armstrong Number - #1134 | Difficulty: Easy | View Code

Remove Vowels from a String - #1119 | Difficulty: Easy | View Code

Number of Days in a Month - #1118 | Difficulty: Easy | View Code

Find K-Length Substrings With No Repeated Characters - #1100 | Difficulty: Medium | View Code

Two Sum Less Than K - #1099 | Difficulty: Easy | View Code

Sum of Digits in the Minimum Number - #1085 | Difficulty: Easy | View Code

Brace Expansion - #1087 | Difficulty: Medium | View Code

Index Pairs of a String - #1065 | Difficulty: Easy | View Code

High Five - #1086 | Difficulty: Easy | View Code

Confusing Number - #1056 | Difficulty: Easy | View Code

Buddy Strings - #859 | Difficulty: Easy | View Code

Insert into a Sorted Circular Linked List - #708 | Difficulty: Medium | View Code

Cheapest Flights Within K Stops - #787 | Difficulty: Medium | View Code

Sentence Similarity - #734 | Difficulty: Easy | View Code

Design Compressed String Iterator - #604 | Difficulty: Easy | View Code

Most Frequent Subtree Sum - #508 | Difficulty: Medium | View Code

Arranging Coins - #441 | Difficulty: Easy | View Code

Find All Anagrams in a String - #438 | Difficulty: Medium | View Code

Valid Word Square - #422 | Difficulty: Easy | View Code

Plus One Linked List - #369 | Difficulty: Medium | View Code

Find Leaves of Binary Tree - #366 | Difficulty: Medium | View Code

Moving Average from Data Stream - #346 | Difficulty: Easy | View Code

Nested List Weight Sum - #339 | Difficulty: Easy | View Code

Inorder Successor in BST - #285 | Difficulty: Medium | View Code

Encode and Decode Strings - #271 | Difficulty: Medium | View Code

Meeting Rooms II - #253 | Difficulty: Medium | View Code

Meeting Rooms - #252 | Difficulty: Easy | View Code

House Robber - #198 | Difficulty: Easy | View Code

Balanced Binary Tree - #110 | Difficulty: Easy | View Code

3Sum - #15 | Difficulty: Medium | View Code

July

Number of Equivalent Domino Pairs - #1128 | Difficulty: Easy | View Code

Lowest Common Ancestor of Deepest Leaves - #1123 | Difficulty: Medium | View Code

Relative Sort Array - #1122 | Difficulty: Easy | View Code

Defanging an IP Address - #1108 | Difficulty: Easy | View Code

Print in Order - #1114 | Difficulty: Easy | View Code

Print FooBar Alternately - #1115 | Difficulty: Medium | View Code

Binary Prefix Divisible By 5 - #1018 | Difficulty: Easy | View Code

Smallest Subtree with all the Deepest Nodes - #865 | Difficulty: Medium | View Code

Daily Temperatures - #739 | Difficulty: Medium | View Code

Find Duplicate Subtrees - #652 | Difficulty: Medium | View Code

Reshape the Matrix - #566 | Difficulty: Easy | View Code

Subarray Sum Equals K - #560 | Difficulty: Medium | View Code

Continuous Subarray Sum - #523 | Difficulty: Medium | View Code

Serialize and Deserialize BST - #449 | Difficulty: Medium | View Code

Serialize and Deserialize Binary Tree - #297 | Difficulty: Hard | View Code

Lowest Common Ancestor of a Binary Tree - #236 | Difficulty: Medium | View Code

Reverse Bits - #190 | Difficulty: Easy | View Code

Reorder List - #143 | Difficulty: Medium | View Code

Populating Next Right Pointers in Each Node - #116 | Difficulty: Medium | View Code

Flatten Binary Tree to Linked List - #114 | Difficulty: Medium | View Code

Set Matrix Zeroes - #73 | Difficulty: Medium | View Code

Maximum Subarray - #53 | Difficulty: Easy | View Code

First Missing Positive - #41 | Difficulty: Hard | View Code

Merge Two Sorted Lists - #21 | Difficulty: Easy | View Code

ZigZag Conversion - #6 | Difficulty: Medium | View Code

Longest Palindromic Substring - #5 | Difficulty: Medium | View Code

June

Duplicate Zeros - #1089 | Difficulty: Easy | View Code

Letter Tile Possibilities - #1079 | Difficulty: Medium | View Code

Occurrences After Bigram - #1078 | Difficulty: Easy | View Code

Greatest Common Divisor of Strings - #1071 | Difficulty: Easy | View Code

Distant Barcodes - #1054 | Difficulty: Medium | View Code

Partition Array Into Three Parts With Equal Sum - #1013 | Difficulty: Easy | View Code

Add to Array-Form of Integer - #989 | Difficulty: Easy | View Code

Time Based Key-Value Store - #981 | Difficulty: Medium | View Code

Partition Array into Disjoint Intervals - #915 | Difficulty: Medium | View Code

X of a Kind in a Deck of Cards - #914 | Difficulty: Easy | View Code

Leaf-Similar Trees - #872 | Difficulty: Easy | View Code

Design Circular Queue - #622 | Difficulty: Medium | View Code

Find Smallest Letter Greater Than Target - #744 | Difficulty: Easy | View Code

1-bit and 2-bit Characters - #717 | Difficulty: Easy | View Code

Permutation in String - #567 | Difficulty: Medium | View Code

Convert BST to Greater Tree - #538 | Difficulty: Easy | View Code

Battleships in a Board - #419 | Difficulty: Medium | View Code

Maximum Gap - #164 | Difficulty: Hard | View Code

Reverse Linked List II - #92 | Difficulty: Medium | View Code

Subsets II - #90 | Difficulty: Medium | View Code

Partition List - #86 | Difficulty: Medium | View Code

Spiral Matrix - #54 | Difficulty: Medium | View Code

Rotate Image - #48 | Difficulty: Medium | View Code

Reverse Nodes in k-Group - #25 | Difficulty: Hard | View Code

Merge k Sorted Lists - #23 | Difficulty: Hard | View Code

Integer to Roman - #12 | Difficulty: Medium | View Code

May

Height Checker - #1051 | Difficulty: Easy | View Code

Remove All Adjacent Duplicates In String - #1047 | Difficulty: Easy | View Code

Last Stone Weight - #1046 | Difficulty: Easy | View Code

Uncrossed Lines - #1035 | Difficulty: Medium | View Code

Matrix Cells in Distance Order - #1030 | Difficulty: Easy | View Code

Sum of Root To Leaf Binary Numbers - #1022 | Difficulty: Easy | View Code

Next Greater Node In Linked List - #1019 | Difficulty: Medium | View Code

Sum of Even Numbers After Queries - #985 | Difficulty: Easy | View Code

Verifying an Alien Dictionary - #953 | Difficulty: Easy | View Code

Valid Mountain Array - #941 | Difficulty: Easy | View Code

Increasing Order Search Tree - #897 | Difficulty: Easy | View Code

Goat Latin - #824 | Difficulty: Easy | View Code

Binary Tree Pruning - #814 | Difficulty: Medium | View Code

Custom Sort String - #791 | Difficulty: Medium | View Code

Longest Word in Dictionary - #720 | Difficulty: Easy | View Code

Repeated String Match - #686 | Difficulty: Easy | View Code

Reverse String II - #541 | Difficulty: Easy | View Code

Repeated Substring Pattern - #459 | Difficulty: Easy | View Code

Sum of Left Leaves - #404 | Difficulty: Easy | View Code

Valid Perfect Square - #367 | Difficulty: Easy | View Code

Wiggle Sort II - #324 | Difficulty: Medium | View Code

Bulb Switcher - #319 | Difficulty: Medium | View Code

Range Sum Query - Mutable - #307 | Difficulty: Medium | View Code

First Bad Version - #278 | Difficulty: Easy | View Code

Search a 2D Matrix II - #240 | Difficulty: Medium | View Code

Product of Array Except Self - #238 | Difficulty: Medium | View Code

Kth Largest Element in an Array - #215 | Difficulty: Medium | View Code

Isomorphic Strings - #205 | Difficulty: Easy | View Code

Find Peak Element - #162 | Difficulty: Medium | View Code

Path Sum - #112 | Difficulty: Easy | View Code

Remove Duplicates from Sorted Array II - #80 | Difficulty: Medium | View Code

Search a 2D Matrix - #74 | Difficulty: Medium | View Code

Group Anagrams - #49 | Difficulty: Medium | View Code

Find First and Last Position of Element in Sorted Array - #34 | Difficulty: Medium | View Code

Longest Common Prefix - #14 | Difficulty: Easy | View Code

April

Two City Scheduling - #1029 | Difficulty: Easy | View Code

Remove Outermost Parentheses - #1021 | Difficulty: Easy | View Code

Largest Perimeter Triangle - #976 | Difficulty: Easy | View Code

Check Completeness of a Binary Tree - #958 | Difficulty: Medium | View Code

Sort an Array - #912 | Difficulty: Medium | View Code

Binary Gap - #868 | Difficulty: Easy | View Code

Letter Case Permutation - #784 | Difficulty: Easy | View Code

Binary Search - #704 | Difficulty: Easy | View Code

Kth Largest Element in a Stream - #703 | Difficulty: Easy | View Code

Flatten a Multilevel Doubly Linked List - #430 | Difficulty: Medium | View Code

Degree of an Array - #697 | Difficulty: Easy | View Code

Implement Magic Dictionary - #676 | Difficulty: Medium | View Code

Array Partition I - #561 | Difficulty: Easy | View Code

String Compression - #443 | Difficulty: Easy | View Code

Random Pick Index - #398 | Difficulty: Medium | View Code

Integer Replacement - #397 | Difficulty: Medium | View Code

Shuffle an Array - #384 | Difficulty: Medium | View Code

Linked List Random Node - #382 | Difficulty: Medium | View Code

Kth Smallest Element in a Sorted Matrix - #378 | Difficulty: Medium | View Code

Find K Pairs with Smallest Sums - #373 | Difficulty: Medium | View Code

Sum of Two Integers - #371 | Difficulty: Medium | View Code

Power of Four - #342 | Difficulty: Easy | View Code

Flatten Nested List Iterator - #341 | Difficulty: Medium | View Code

Power of Three - #326 | Difficulty: Easy | View Code

Range Sum Query - Immutable - #303 | Difficulty: Easy | View Code

Peeking Iterator - #284 | Difficulty: Medium | View Code

Power of Two - #231 | Difficulty: Easy | View Code

Contains Duplicate II - #219 | Difficulty: Easy | View Code

Binary Tree Right Side View - #199 | Difficulty: Medium | View Code

Number of 1 Bits - #191 | Difficulty: Easy | View Code

Two Sum II - Input array is sorted - #167 | Difficulty: Easy | View Code

Find Minimum in Rotated Sorted Array II - #154 | Difficulty: Hard | View Code

Symmetric Tree - #101 | Difficulty: Easy | View Code

Merge Sorted Array - #88 | Difficulty: Easy | View Code

Subsets - #78 | Difficulty: Medium | View Code

Sort Colors - #75 | Difficulty: Medium | View Code

Merge Intervals - #56 | Difficulty: Medium | View Code

March

Complement of Base 10 Integer - #1009 | Difficulty: Easy | View Code

Find Common Characters - #1002 | Difficulty: Easy | View Code

Cousins in Binary Tree - #993 | Difficulty: Easy | View Code

Vertical Order Traversal of a Binary Tree - #987 | Difficulty: Medium | View Code

Reorder Data in Log Files - #937 | Difficulty: Easy | View Code

Minimum Add to Make Parentheses Valid - #921 | Difficulty: Medium | View Code

Middle of the Linked List - #876 | Difficulty: Easy | View Code

Design Linked List - #707 | Difficulty: Medium | View Code

Minimum Distance Between BST Nodes - #783 | Difficulty: Easy | View Code

Toeplitz Matrix - #766 | Difficulty: Easy | View Code

N-ary Tree Postorder Traversal - #590 | Difficulty: Easy | View Code

N-ary Tree Level Order Traversal - #429 | Difficulty: Medium | View Code

Split Linked List in Parts - #725 | Difficulty: Medium | View Code

Longest Continuous Increasing Subsequence - #674 | Difficulty: Easy | View Code

2 Keys Keyboard - #650 | Difficulty: Medium | View Code

Average of Levels in Binary Tree - #637 | Difficulty: Easy | View Code

Merge Two Binary Trees - #617 | Difficulty: Easy | View Code

Longest Harmonious Subsequence - #594 | Difficulty: Easy | View Code

Find Bottom Left Tree Value - #513 | Difficulty: Medium | View Code

Next Greater Element II - #503 | Difficulty: Medium | View Code

Find Mode in Binary Search Tree - #501 | Difficulty: Easy | View Code

Next Greater Element I - #496 | Difficulty: Easy | View Code

Add Two Numbers II - #445 | Difficulty: Medium | View Code

Find All Duplicates in an Array - #442 | Difficulty: Medium | View Code

Add Strings - #415 | Difficulty: Easy | View Code

Longest Palindrome - #409 | Difficulty: Easy | View Code

Design Twitter - #355 | Difficulty: Medium | View Code

Find the Duplicate Number - #287 | Difficulty: Medium | View Code

Sliding Window Maximum - #239 | Difficulty: Hard | View Code

Implement Queue using Stacks - #232 | Difficulty: Easy | View Code

Implement Stack using Queues - #225 | Difficulty: Easy | View Code

Count Complete Tree Nodes - #222 | Difficulty: Medium | View Code

Reverse Linked List - #206 | Difficulty: Easy | View Code

Happy Number - #202 | Difficulty: Easy | View Code

Rotate Array - #189 | Difficulty: Easy | View Code

Repeated DNA Sequences - #187 | Difficulty: Medium | View Code

Binary Search Tree Iterator - #173 | Difficulty: Medium | View Code

Min Stack - #155 | Difficulty: Easy | View Code

Binary Tree Postorder Traversal - #145 | Difficulty: Hard | View Code

Binary Tree Preorder Traversal - #144 | Difficulty: Medium | View Code

Linked List Cycle II - #142 | Difficulty: Medium | View Code

Linked List Cycle - #141 | Difficulty: Easy | View Code

Best Time to Buy and Sell Stock - #121 | Difficulty: Easy | View Code

Minimum Depth of Binary Tree - #111 | Difficulty: Easy | View Code

Binary Tree Level Order Traversal II - #107 | Difficulty: Easy | View Code

Binary Tree Zigzag Level Order Traversal - #103 | Difficulty: Medium | View Code

Binary Tree Level Order Traversal - #102 | Difficulty: Medium | View Code

Same Tree - #100 | Difficulty: Easy | View Code

Binary Tree Inorder Traversal - #94 | Difficulty: Medium | View Code

Add Binary - #67 | Difficulty: Easy | View Code

Rotate List - #61 | Difficulty: Medium | View Code

Valid Parentheses - #20 | Difficulty: Easy | View Code

February

Available Captures for Rook - #999 | Difficulty: Easy | View Code

Find the Town Judge - #997 | Difficulty: Easy | View Code

Univalued Binary Tree - #965 | Difficulty: Easy | View Code

Design HashSet - #705 | Difficulty: Easy | View Code

Flood Fill - #733 | Difficulty: Easy | View Code

Find Pivot Index - #724 | Difficulty: Easy | View Code

Top K Frequent Words - #692 | Difficulty: Medium | View Code

Replace Words - #648 | Difficulty: Medium | View Code

Minimum Absolute Difference in BST - #530 | Difficulty: Easy | View Code

Max Consecutive Ones - #485 | Difficulty: Easy | View Code

License Key Formatting - #482 | Difficulty: Easy | View Code

Find All Numbers Disappeared in an Array - #448 | Difficulty: Easy | View Code

Find the Difference - #389 | Difficulty: Easy | View Code

First Unique Character in a String - #387 | Difficulty: Easy | View Code

Top K Frequent Elements - #347 | Difficulty: Medium | View Code

Reverse String - #344 | Difficulty: Easy | View Code

Add and Search Word - Data structure design - #211 | Difficulty: Medium | View Code

Excel Sheet Column Number - #171 | Difficulty: Easy | View Code

Sort List - #148 | Difficulty: Medium | View Code

LRU Cache - #146 | Difficulty: Medium | View Code

Combinations - #77 | Difficulty: Medium | View Code

Container With Most Water - #11 | Difficulty: Medium | View Code

January

Squares of a Sorted Array - #977 | Difficulty: Easy | View Code

K Closest Points to Origin - #973 | Difficulty: Medium | View Code

Fibonacci Number - #509 | Difficulty: Easy | View Code

Largest Time for Given Digits - #949 | Difficulty: Easy | View Code

DI String Match - #942 | Difficulty: Easy | View Code

Range Sum of BST - #938 | Difficulty: Easy | View Code

Number of Recent Calls - #933 | Difficulty: Easy | View Code

Monotonic Array - #896 | Difficulty: Easy | View Code

Employee Importance - #690 | Difficulty: Easy | View Code

Valid Palindrome II - #680 | Difficulty: Easy | View Code

Set Mismatch - #645 | Difficulty: Easy | View Code

Minimum Index Sum of Two Lists - #599 | Difficulty: Easy | View Code

Single Element in a Sorted Array - #540 | Difficulty: Medium | View Code

Detect Capital - #520 | Difficulty: Easy | View Code

Find Largest Value in Each Tree Row - #515 | Difficulty: Medium | View Code

Third Maximum Number - #414 | Difficulty: Easy | View Code

Single Number III - #260 | Difficulty: Medium | View Code

Delete Node in a Linked List - #237 | Difficulty: Easy | View Code

Remove Linked List Elements - #203 | Difficulty: Easy | View Code

Intersection of Two Linked Lists - #160 | Difficulty: Easy | View Code

Single Number II - #137 | Difficulty: Medium | View Code

Permutations - #46 | Difficulty: Medium | View Code

Reverse Integer - #7 | Difficulty: Easy | View Code

2018

December

N-Repeated Element in Size 2N Array - #961 | Difficulty: Easy | View Code

Max Increase to Keep City Skyline - #807 | Difficulty: Medium | View Code

November

Sort Array By Parity II - #922 | Difficulty: Easy | View Code

Reverse Only Letters - #917 | Difficulty: Easy | View Code

Stone Game - #877 | Difficulty: Medium | View Code

Peak Index in a Mountain Array - #852 | Difficulty: Easy | View Code

Maximum Depth of N-ary Tree - #559 | Difficulty: Easy | View Code

Shortest Completing Word - #748 | Difficulty: Easy | View Code

Baseball Game - #682 | Difficulty: Easy | View Code

Intersection of Two Arrays II - #350 | Difficulty: Easy | View Code

Intersection of Two Arrays - #349 | Difficulty: Easy | View Code

Valid Sudoku - #36 | Difficulty: Medium | View Code

Swap Nodes in Pairs - #24 | Difficulty: Medium | View Code

October

Unique Email Addresses - #929 | Difficulty: Easy | View Code

Find and Replace Pattern - #890 | Difficulty: Medium | View Code

Subdomain Visit Count - #811 | Difficulty: Easy | View Code

Rotated Digits - #788 | Difficulty: Easy | View Code

Maximum Product of Three Numbers - #628 | Difficulty: Easy | View Code

Fizz Buzz - #412 | Difficulty: Easy | View Code

Reverse Words in a String - #151 | Difficulty: Medium | View Code

Climbing Stairs - #70 | Difficulty: Easy | View Code

September

Sort Array By Parity - #905 | Difficulty: Easy | View Code

Uncommon Words from Two Sentences - #884 | Difficulty: Easy | View Code

Lemonade Change - #860 | Difficulty: Easy | View Code

Shortest Distance to a Character - #821 | Difficulty: Easy | View Code

Search in a Binary Search Tree - #700 | Difficulty: Easy | View Code

Largest Number At Least Twice of Others - #747 | Difficulty: Easy | View Code

Max Area of Island - #695 | Difficulty: Medium | View Code

Second Minimum Node In a Binary Tree - #671 | Difficulty: Easy | View Code

Two Sum IV - Input is a BST - #653 | Difficulty: Easy | View Code

Binary Tree Tilt - #563 | Difficulty: Easy | View Code

Sort Characters By Frequency - #451 | Difficulty: Medium | View Code

Number of Segments in a String - #434 | Difficulty: Easy | View Code

Lexicographical Numbers - #386 | Difficulty: Medium | View Code

Ransom Note - #383 | Difficulty: Easy | View Code

Logger Rate Limiter - #359 | Difficulty: Easy | View Code

Reverse Vowels of a String - #345 | Difficulty: Easy | View Code

Odd Even Linked List - #328 | Difficulty: Medium | View Code

Word Pattern - #290 | Difficulty: Easy | View Code

Valid Anagram - #242 | Difficulty: Easy | View Code

Kth Smallest Element in a BST - #230 | Difficulty: Medium | View Code

Majority Element II - #229 | Difficulty: Medium | View Code

Contains Duplicate - #217 | Difficulty: Easy | View Code

Number of Islands - #200 | Difficulty: Medium | View Code

Find Minimum in Rotated Sorted Array - #153 | Difficulty: Medium | View Code

Maximum Depth of Binary Tree - #104 | Difficulty: Easy | View Code

Validate Binary Search Tree - #98 | Difficulty: Medium | View Code

Remove Duplicates from Sorted List - #83 | Difficulty: Easy | View Code

Remove Duplicates from Sorted List II - #82 | Difficulty: Medium | View Code

Search in Rotated Sorted Array II - #81 | Difficulty: Medium | View Code

Permutation Sequence - #60 | Difficulty: Hard | View Code

Multiply Strings - #43 | Difficulty: Medium | View Code

Remove Element - #27 | Difficulty: Easy | View Code

Remove Nth Node From End of List - #19 | Difficulty: Medium | View Code

Palindrome Number - #9 | Difficulty: Easy | View Code

Add Two Numbers - #2 | Difficulty: Medium | View Code

Two Sum - #1 | Difficulty: Easy | View Code

August

Minimum Moves to Equal Array Elements II - #462 | Difficulty: Medium | View Code

Guess Number Higher or Lower - #374 | Difficulty: Easy | View Code

Missing Number - #268 | Difficulty: Easy | View Code

Palindrome Linked List - #234 | Difficulty: Easy | View Code

Plus One - #66 | Difficulty: Easy | View Code

Remove Duplicates from Sorted Array - #26 | Difficulty: Easy | View Code

Median of Two Sorted Arrays - #4 | Difficulty: Hard | View Code

July

Transpose Matrix - #867 | Difficulty: Easy | View Code

Backspace String Compare - #844 | Difficulty: Easy | View Code

Flipping an Image - #832 | Difficulty: Easy | View Code

Number of Lines To Write String - #806 | Difficulty: Easy | View Code

Unique Morse Code Words - #804 | Difficulty: Easy | View Code

Rotate String - #796 | Difficulty: Easy | View Code

To Lower Case - #709 | Difficulty: Easy | View Code

Valid Parenthesis String - #678 | Difficulty: Medium | View Code

Relative Ranks - #506 | Difficulty: Easy | View Code

Hamming Distance - #461 | Difficulty: Easy | View Code

Counting Bits - #338 | Difficulty: Medium | View Code

June

Most Common Word - #819 | Difficulty: Easy | View Code

Find K Closest Elements - #658 | Difficulty: Medium | View Code

Search in Rotated Sorted Array - #33 | Difficulty: Medium | View Code