LintCode - Add Two Numbers

Web Link

http://www.lintcode.com/en/problem/add-two-numbers/

Description

You have two numbers represented by a linked list, where each node contains a single digit. The digits are stored in reverse order, such that the 1’s digit is at the head of the list. Write a function that adds the two numbers and returns the sum as a linked list.

Example
Given 7->1->6 + 5->9->2. That is, 617 + 295.

Return 2->1->9. That is 912.

Given 3->1->5 and 5->9->2, return 8->0->8.

Code - C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    /**
     * @param l1: the first list
     * @param l2: the second list
     * @return: the sum list of l1 and l2 
     */
    ListNode *addLists(ListNode *l1, ListNode *l2) {
        // write your code here
        ListNode dummy(0);
        ListNode*p = &dummy;
        int cn = 0;
        while(l1||l2){
            int val = cn + (l1 ? l1->val : 0) + (l2 ? l2->val : 0);
            cn = val / 10;
            val = val % 10;
            p->next = new ListNode(val);
            p = p->next;
            if(l1){
                l1 = l1->next;
            }
            if(l2){
                l2 = l2->next;
            }
        }
        if(cn != 0){
            p->next = new ListNode(cn);
            p = p->next;
        }
        return dummy.next;
    }
};

Tips:

• None