LeetCode Add Two Numbers

题目链接：http://oj.leetcode.com/problems/add-two-numbers/

描述：

Add Two Numbers

 

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

题目意思：求用两个链表表示的数字的和。

解法：

本题很简单，模拟加法，时间复杂度O(n), n为两个链表表示的数位的最大位数。

代码如下：

    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {        // IMPORTANT: Please reset any member data you declared, as        // the same Solution instance will be reused for each test case.    ListNode head(-1);    ListNode *p = &head;    if(l1 == NULL) return l2;    if(l2 == NULL) return l1;    ListNode *p1 = l1;    ListNode *p2 = l2;    int carry = 0;    while(p1 || p2){    const int num1 = p1 == NULL ? 0 : p1->val;    const int num2 = p2 == NULL ? 0 : p2->val;        p1 = p1 == NULL? NULL : p1->next;    p2 = p2 == NULL? NULL : p2->next;        int sum = num1 + num2 + carry;    carry = sum / 10;    sum %= 10;    ListNode *new_node = new ListNode(sum);    p->next = new_node;    p = p->next;    }        if(carry > 0){    ListNode *new_node = new ListNode(carry);    p->next = new_node;    }    return head.next;    }