Add Two Numbers

leetcode merge

Add Two Numbers

题目链接

题目大意:

You are given two linked lists representing two non-negative numbers. 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.

example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

题目翻译：

给定两个链表表示两个非负数。数字逆序存储，每个节点包含一个单一的数字。计算两个数的和，并以链表的形式返还。

分析：

要考虑进位。表示结果的结点要new出来。

Code

/**
 * 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* anno = NULL;
        if(l1 == anno) return l2;
        if(l2 == anno) return l1;
        ListNode *res = NULL;
        ListNode *p = NULL;
        int las = 0;
        int v;
        const int base = 10;
        while(l1 != anno && l2 != anno) {
            las += l1->val;
            las += l2->val;
            v = las % base;
            if(res == NULL) {
                res = new ListNode(v);
                p = res;
            } else {
                p->next = new ListNode(v);
                p = p->next;
            }
            // refresh
            l1 = l1->next;
            l2 = l2->next;
            las = las / base;
        }
        while(l1 != anno) {
            las += l1->val;
            v = las % base;
            p->next = new ListNode(v);
            p = p->next;
            // refresh
            las = las / base;
            l1 = l1->next;
        }
        while(l2 != anno) {
            las += l2->val;
            int v = las % base;
            p->next = new ListNode(v);
            p = p->next;
            // refresh
            las = las / base;
            l2 = l2->next;
        }
        // don't forget the last one
        if(las >= 1) {
            p->next = new ListNode(las);
            p = p->next;
        }
        return res;
    }
};