Description

tags: Linked list, Math

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.
Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

Solution

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* ret = new ListNode(0);
        ListNode* head = ret;
        int carry = 0;
        while (l1 != NULL || l2 != NULL) {
            int x = (l1 == NULL? 0 : l1->val);
            int y = (l2 == NULL? 0 : l2->val);
            int sum = x + y + carry;
            ListNode* current = new ListNode(sum % 10);
            ret->next = current;
            ret = ret->next;
            carry = sum / 10;
            l1 = (l1 == NULL? l1 : l1->next);
            l2 = (l2 == NULL? l2 : l2->next);
        }
        if (carry != 0) {
            ListNode* current = new ListNode(1);
            ret->next = current;
        }
        return head->next;
    }
};

Analysis

Clever Handle of different situations in one while loop.