JavaWithDsa/DoublyLinkedList.java at master · vishallovecode/JavaWithDsa · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
public class doublyLinkedList {
    Node head ;
    class Node  {
        int data ;
        Node next;
        Node prev;
        Node(int data) {
            this.data = data;
            prev  = null;
            next = null;
        }
    }
    public void display() {
        Node ptr;
        ptr =head;
        while(ptr!=null) {
            System.out.println(ptr.data);
            ptr= ptr.next;
        }
    }
    public void insertFirst(int data) {
        // if there is already node exist
        // else there is no node exist

        // how should i know the linked list is empty ??

        Node newNode  = new Node(data);
        if(head==null) {
            head= newNode;
            // head.next =null;
            // head.prev  =null;
        } else {
                // here head is pointing to the firts node of the linked list we want to add
                // Node before that node, so our newnode next should point to the first node of current linked list before adding the newNode
                head.prev  =  newNode;
                newNode.next = head;
                head = newNode;
        }
    }


    public void insertLast (int data) {
        Node newNode  = new Node(data);
        Node ptr ;
         ptr=head;
         if(head ==null) {
            head= newNode;
         }  else {
                     // traversing till the end of the loop
            while(ptr.next!=null) {
                ptr = ptr.next;
            }
            // in this my ptr will be last node;
            ptr.next = newNode;
            newNode.prev = ptr;
         }
    }

// public void insertAfterNode() {

// }
// public void insertBeforeNode() {

// }

// public void insertAtGivenIndex() {

// }


// delete the node after given node
// delete the node before given node
// delete the node in given index


public void deleteFromFirst() {
    if(head==null  ) {
        System.out.println("Overflow!!!!!");
        return;
    }  else {
        if(head.next !=null) {
            head.next.prev  =null;
        }
        if(head.next==null) {
            System.out.println("Deleting last|| first left node");
        }
        head = head.next;
    }
}

public void deleteFromLast () {

  if(head.next==null) {
    head =null;
    return ;
  }
Node ptr   = head;
while(ptr.next!=null) {
    ptr= ptr.next;
}
ptr.prev.next =  null;
}

public static void main(String[] args) {
    doublyLinkedList dl  = new doublyLinkedList();
    dl.insertLast(600);
    dl.insertFirst(100); // node1
    dl.insertFirst(200); // node2
    dl.insertFirst(300); // node3
    dl.insertFirst(500);
    dl.insertLast(400);
    dl.deleteFromLast();
    dl.deleteFromLast();
    dl.deleteFromLast();
    dl.deleteFromLast();
    dl.deleteFromLast();
    dl.deleteFromLast();


          // last element delete

    // dl.deleteFromFirst();


    dl.display(); //
}
}

// [500]->[300]->[200]->[100]->[600]-> [400]


//                     Node1                                   Node2                       Node3
// // head--->[prev->null , 200 , next --->Node1]-->[prev==node1, 100 , next=node3]-->[prev->node2 , 400, next=null]


// //ptr.next==null

// // ptr.prev.next = null