LeetCode: Add Two Numbers 解题报告

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

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

解答：

比较简单，直接用2个指针往后移动，并且将2个list的值相加，并且计算上carry值。注意，在while循环中加上carry == 1的判断，这样可以自动在链尾加上carry 的值。

 package Algorithms.list;

 import Algorithms.algorithm.others.ListNode;

 /**

  * Definition for singly-linked list.

  * public class ListNode {

  *     int val;

  *     ListNode next;

  *     ListNode(int x) {

  *         val = x;

  *         next = null;

  *     }

  * }

  */

 public class AddTwoNumbers {

     public static void main(String[] str) {

         ListNode n1 = new ListNode(9);

         ListNode l1 = new ListNode(1);

         ListNode l2 = new ListNode(9);

         ListNode l3 = new ListNode(9);

         ListNode l4 = new ListNode(9);

         ListNode l5 = new ListNode(9);

         ListNode l6 = new ListNode(9);

         ListNode l7 = new ListNode(9);

         ListNode l8 = new ListNode(9);

         ListNode l9 = new ListNode(9);

         ListNode l10 = new ListNode(9);

         l1.next = l2;

         l2.next = l3;

         l3.next = l4;

         l4.next = l5;

         l5.next = l6;

         l6.next = l7;

         l7.next = l8;

         l8.next = l9;

         l9.next = l10;

         System.out.println(addTwoNumbers(n1, l1).toString());

     }

     public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {

         if (l1 == null || l2 == null) {

             return null;

         }

         ListNode dummy = new ListNode(0);

         ListNode tail = dummy;

         int carry = 0;

         while (l1 != null || l2 != null || carry == 1) {

             int sum = carry;

             if (l1 != null) {

                 sum += l1.val;

                 l1 = l1.next;

             }

             if (l2 != null) {

                 sum += l2.val;

                 l2 = l2.next;

             }

             carry = sum / 10;

             // create a new node and add it to the tail.

             ListNode cur = new ListNode(sum % 10);

             tail.next = cur;

             tail = tail.next;

         }

         return dummy.next;

     }

 }

代码：

AddTwoNumbers

巴特西

LeetCode: Add Two Numbers 解题报告

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