LeetCode-Add Two Numbers

LeetCode-Add Two Numbers

Description

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.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode l = new ListNode(0);
        ListNode p = new ListNode(0);
        l = p;
        //進位標誌
        int flag = 0;
        while(l1 != null || l2 != null){
            int x = (l1 != null) l1.val : 0;
            int y = (l2 != null) l2.val : 0;
            ListNode temp = new ListNode(0);
            //計算過程中要加上進位標誌
            temp.val = x + y + flag;
            if(temp.val >= 10){
                temp.val = temp.val % 10;
                flag = 1;
            } else 
                flag = 0;
            p.next = temp;
            p = p.next;
            l1 = l1.next;
            l2 = l2.next;
        }
        //如果最後存在進位，最高位置位1
        if (flag == 1){
            p.next = new ListNode(1);
        }
        return l.next;
    }
}

Note

這個是一個加法模擬運算問題，使用一個單項鍊表來模擬加法問題。鏈表從頭到尾一次是個十百千萬…在加法過程中一定會存在進位的問題，這時我們通過一個flag來充當進位標誌，然後按照從個位開始進行累加，然後不斷的把計算結果添加到鏈表中即可。