Add Two Numbers

来源：互联网发布：react 引入js文件编辑：程序博客网时间：2024/06/04 18:42

1.问题：

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

Illustration of Adding two numbers

Figure 1. Visualization of the addition of two numbers: $342 + 465 = 807$ .
Each node contains a single digit and the digits are stored in reverse order.

译：将两组数字分别存入到两个不带头节点的链表中，存入的方式: 依次去取出最低位，逆序放入链表中。

2 方法： [ me ]

思想: 两条链表节点数目不一样， a表节点多, b表节点少, len（a）-len（b） = n，那么假想给b“添加”n个节点，节点中的值都为0。此时，a表和b表长度相同了，对应节点一次增加（注意进位）, 到最高位相加（最后一位相加）时，需要判断相加之和是否大于10，大于10则需要进位。

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     struct ListNode *next; * }; */struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {    struct ListNode* head = NULL;    struct ListNode* tail = NULL;    int overflow = 0;    // 两条链表,以节点多的链表为基础。为 节点少的链表 填充val=0 .    while(l1 || l2)    {        int one = (l1 == NULL) ? 0: l1->val;        int two = (l2 == NULL) ? 0: l2->val;        int node_result = -1;        int sum = one + two + overflow;        node_result = sum %10;        overflow = sum /10;        struct ListNode* newnode = (struct ListNode* )malloc(sizeof(struct ListNode));        if (NULL == newnode)        {            printf("malloc error");        }        // insert into list        newnode->val = node_result;        newnode->next = NULL;        if (NULL == head)         {            head = newnode;            tail = newnode;        }        else        {            tail->next = newnode;            tail = newnode;        }                // update index                l1 = (l1==NULL)?NULL:l1->next;        l2 = (l2==NULL)?NULL:l2->next;    }    // 最后两个数相加的最高位是否为1    if (1 == overflow)    {        struct ListNode* newnode = (struct ListNode* )malloc(sizeof(struct ListNode));        if (NULL == newnode)        {            printf("malloc error");        }        newnode->val = overflow;        newnode->next = NULL;        tail->next = newnode;    }        /* 优化。 "最后两个数相加最高位是否为1" 可以放入while循环中    while(l1 || l2 || overflow)    {        int one = (l1 == NULL) ? 0: l1->val;        int two = (l2 == NULL) ? 0: l2->val;        int node_result = -1;        int sum = one + two + overflow;        node_result = sum %10;        overflow = sum /10;        struct ListNode* newnode = (struct ListNode* )malloc(sizeof(struct ListNode));        if (NULL == newnode)        {            printf("malloc error");        }        // insert into list        newnode->val = node_result;        newnode->next = NULL;        if (NULL == head)         {            head = newnode;            tail = newnode;        }        else        {            tail->next = newnode;            tail = newnode;        }                // update index                l1 = (l1==NULL)?NULL:l1->next;        l2 = (l2==NULL)?NULL:l2->next;    }    */    return head;}

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