Problem difficulty: Medium
Problem description
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]
Solution approach
As we can see those are two reverse order linked lists. The approach is we iterate though the list and adding up each node. We can calculate carry by the sum // 10. Keep iterate until list1 and list2 are none
class Solution:
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
dummyHead = ListNode(0)
tail = dummyHead
carry = 0
while l1 is not None or l2 is not None or carry != 0:
digit1 = l1.val if l1 is not None else 0
digit2 = l2.val if l2 is not None else 0
sum = digit1 + digit2 + carry
digit = sum % 10
carry = sum // 10
newNode = ListNode(digit)
tail.next = newNode
tail = tail.next
l1 = l1.next if l1 is not None else None
l2 = l2.next if l2 is not None else None
result = dummyHead.next
dummyHead.next = None
return result
Source code: https://github.com/hongquan080799/leetcode/tree/master/add_two_number
