LeetCode | 2. Add Two Numbers

题目

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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

即：342 + 465 = 807

我的思路

此题主要要求熟悉链表（可以参考我的一篇译文），理解了链表的定义、遍历和添加节点等方法之后，很容易可以得到结果。注意需要判断当输入的两个链表有可能长度不一致的情况。

代码

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     struct ListNode *next; * }; */struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {    int tmp = 0;    struct ListNode* retls = NULL;    retls = (struct ListNode*)malloc(sizeof(struct ListNode));    if(retls == NULL) {        printf("malloc failed!\n");        return retls;    }    retls->val = 0;    retls->next = NULL;    struct ListNode *curl1 = l1;    struct ListNode *curl2 = l2;    struct ListNode *curret = retls;    while((curl1 != NULL) && (curl2 != NULL)) {        tmp = curret->val + curl1->val + curl2->val;        curret->val = tmp % 10;        if((curl1->next == NULL) && (curl2->next == NULL) && (tmp < 10)) {            curret->next = NULL;        }        else {            // Adding an new item to the end of the retls.            curret->next = (struct ListNode*)malloc(sizeof(struct ListNode));            curret->next->val = tmp / 10;            curret->next->next = NULL;            curret = curret->next;        }        curl1 = curl1->next;        curl2 = curl2->next;    }    while(curl1 != NULL) {        tmp = curret->val + curl1->val;        curret->val = tmp % 10;        if((curl1->next == NULL) && (tmp < 10)) {            curret->next = NULL;        }        else {            curret->next = (struct ListNode*)malloc(sizeof(struct ListNode));            curret->next->val = tmp / 10;            curret->next->next = NULL;            curret = curret->next;        }        curl1 = curl1->next;    }    while(curl2 != NULL) {        tmp = curret->val + curl2->val;        curret->val = tmp % 10;        if((curl2->next == NULL) && (tmp < 10)) {            curret->next = NULL;        }        else {            curret->next = (struct ListNode*)malloc(sizeof(struct ListNode));            curret->next->val = tmp / 10;            curret->next->next = NULL;            curret = curret->next;        }        curl2 = curl2->next;    }    return retls;}