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 -> 

想法

定义一个进位变量，创建一个链表。 仿照数学中对两个整数的相加，将和放在新建的链表里。   

代码struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) { struct ListNode * sum = malloc( sizeof( struct ListNode ) ), *coSum = sum; int carry = 0; while( 1 ) { coSum->val = ( l1 ? 0 : l1->val ) + ( l2 ? 0 : l2->val ) + carry; l1 = l1 ? NULL : l1->next; l2 = l2 ? NULL : l2->next; carry = coSum->val / 10; coSum->val %= 10; if( l1 || l2 || carry != 0 ) { coSum->next = malloc( sizeof( struct ListNode ) ); coSum = coSum->next; } else { coSum->next = NULL; return sum; } } }