[LeetCode] Add Two Numbers

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

 

问题：

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contains 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

 

解题思路：

1）用变量carry记录是否进位

2）从链表头开始计算两链表相应位置上的数字之和

注意

1）输入两链表长度不相等

2）两链表相加之后的结果链表长度可能大于两链表（例如：(9->9) + (1) = (0->0->1)

        public ListNode addTwoNumbers(ListNode l1, ListNode l2){
        ListNode dummyHead = new ListNode(0);
        ListNode p = l1;
        ListNode q = l2;
        ListNode curr = dummyHead;
        int carry = 0;
        while(p != null || q != null){
            int x = (p != null) ? p.val : 0;
            int y = (q != null) ? q.val : 0;
            int digit = carry + x + y;
            curr.next = new ListNode(digit % 10);
            curr = curr.next;
            carry = digit / 10;
            if(p != null){
                p = p.next;
            }
            if(q != null){
                q = q.next;
            }
        }
        if(carry > 0){
            curr.next = new ListNode(carry);
        }
        return dummyHead.next;
    }