leetcode 2. Add Two Numbers

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题目

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.

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

题解

两个指针，向后扫描，注意进位，当到了最后一个节点时，若进位等于1，则应该创建新节点，并赋值为1。 可以使用头结点，以方便while循环规则。

代码

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/**
 * 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) {
        int carry = 0;
        int sum = 0;
        ListNode * res = new ListNode(0);
        ListNode * cur = res;
        while(l1 || l2 || carry)
        {
            sum = carry;
            carry = 0;
            if(l1)
            {
                sum += l1->val;
                l1 = l1->next;
            }
            if(l2)
            {
                sum += l2->val;
                l2 = l2->next;
            }
            if(sum > 9) 
            {
                sum -= 10;
                carry = 1;
            }
            cur->next = new ListNode(sum);
            cur = cur->next;
        }
        ListNode * tmp = res;
        res = res->next;
        delete tmp;
        return res;
    }
};