LeetCode 002

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.

题目读了半天，简单总结一下：两个非空链表代表两个非负整数，并且数字是倒序存放的，每个节点仅有一个数码。把两个数加起来，以链表形式返回。

看了看....这不就是两个大整数相加的题么，换了个链表的马甲。。。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
#define null NULL
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        if(l1 == NULL && l2 == null ){
            return null;
        }
        int ans = 0;
        ListNode *head = null;
        ListNode *tail = null;
        while(l1 != null || l2 != null){
            if(l1 != null){
                ans += l1->val;
                l1 = l1->next;
            }
            if(l2 != null){
                ans += l2->val;
                l2 = l2->next;
            }
            ListNode *p = new ListNode(ans%10);
            ans /= 10;
            if(head == NULL){
                head = p;
                tail = p;
            }else{
                tail->next = p;
                tail = tail->next;
            }
        }
        if(ans!=0){
            ListNode *p = new ListNode(ans);
            tail->next = p;
            tail = tail->next;
        }
        return head;
    }
};