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 contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 0 -> 8 Explanation: 342 + 465 = 807.
Solution in Python
Approach 1: Elementary Math
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode: result = ListNode(0) pre = result carry = 0 while l1 or l2 or carry: value1 = l1.val if l1 else 0 value2 = l2.val if l2 else 0 current = value1 + value2 + carry if current >= 10: cur = ListNode(current-10) carry = 1 else: cur = ListNode(current) carry = 0 pre.next = cur pre = pre.next l1 = l1.next if l1 else None l2 = l2.next if l2 else None if (not l1) and (not l2) and carry: pre.next = ListNode(1) return result.next
- Time complexity: O(max(m, n)). Assume that m and n represents the length of l1 and l2 respectively, the algorithm above iterates at most max(m, n) times.
- Space complexity: O(max(m, n)). The length of the new list is at most max(m, n) + 1.