addTwoNumbers.py

# Add Two Numbers
# You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.
# You may assume the two numbers do not contain any leading zero, except the number 0 itself.


# Example 1:
# Input: l1 = [2,4,3], l2 = [5,6,4]
# Output: [7,0,8]
# Explanation: 342 + 465 = 807.

# Example 2:
# Input: l1 = [0], l2 = [0]
# Output: [0]

# Example 3:
# Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
# Output: [8,9,9,9,0,0,0,1]


class ListNode(object):
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def addTwoNumbers(l1, l2):
    head = ListNode()
    current = head
    carry = 0
    while (l1 != None or l2 != None or carry != 0):
        l1_value = l1.val if l1 else 0
        l2_value = l2.val if l2 else 0
        total = l1_value + l2_value + carry
        current.next = ListNode(total % 10)
        carry = total // 10
        l1 = l1.next if l1 else None
        l2 = l2.next if l2 else None
        current = current.next
    return head.next


l1 = [2, 4, 6]
l2 = [5, 6, 4]
print(addTwoNumbers(l1, l2))