add2numbers.py

class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None
        self.prev = None
    def __str__(self):
        if not self.next: return str(self.val)
        else: return str(self.val) + " " + str(self.next)
    def __repr__(self):
        return self.__str__()
    def __eq__(self,other):
        return self.__str__() == other.__str__()
def addTwoNumbers(l1, l2, previous_carry = 0):
    p1 = l1 # watchvar ref:l1:btree p1
    p2 = l2 # watchvar ref:l2:btree p2
    carry = 0 # watchvar carry
    head = ListNode(-1) # watchvar btree:prev:next:val head
    tail = head # watchvar ref:head:btree tail
    while p1 or p2 or carry:
        v1 = p1.val if p1 else 0 # watchvar v1
        v2 = p2.val if p2 else 0 # watchvar v2
        n = v1 + v2 + carry
        carry = n // 10
        n = n % 10
        node = ListNode(n)
        if tail:
            tail.next = node
            tail = node
        else:
            head = node
            tail = node
        p1 = p1.next if p1 else None
        p2 = p2.next if p2 else None
    return head.next




def go():
    # https://leetcode.com/problems/add-two-numbers/
    a = ListNode(10) # watchvar btree:prev:next:val a
    b= ListNode(22)  # watchvar a
    c = ListNode(30) # watchvar btree:prev:next:val c
    d = ListNode(43) # watchvar c
    a.next = b 
    c.next = d 
    addTwoNumbers(a,c)