LeetCode 2. Add Two Numbers

原题描述

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.

Example

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) 
Output: 7 -> 0 -> 8 
Explanation: 342 + 465 = 807.

 

题目大意

有两个单链表，代表两个非负数，每一个节点代表一个数位，数字是反向存储的，即第一个结点表示最低位，最后一个结点表示最高位。求两个数的相加和，并且以链表形式返回。

 

解题思路

对两个链表都从第一个开始处理，进行相加，结果再除以10求商，作为下一位相加的进位，同时记录余数，作为本位的结果，一直处理，直到所有的结点都处理完。

class Solution { 
 
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) { 
        ListNode pre = new ListNode(0); 
        ListNode head = pre; 
        int carry = 0; 
        while(l1!=null || l2!=null || carry!=0){ 
            ListNode node = new ListNode(0); 
            // 如何某一个链表为空，则用0代替 
            int sum = (l1==null? 0: l1.val) + (l2==null? 0: l2.val) + carry; 
            // 取余 
            node.val = sum % 10; 
            // 计算进位值 
            carry = sum / 10; 
            pre.next = node; 
            pre = node; 
 
            l1 = (l1==null? l1: l1.next); 
            l2 = (l2==null? l2: l2.next); 
        } 
        return head.next; 
    } 
}