Lc 2 - Add Two Numbers
2016-09-21 05:22
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Description
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.Example
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)Output: 7 -> 0 -> 8
MySolution
public class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { ListNode sentinel=new ListNode(0); int sum=0; ListNode temp1=l1; ListNode temp2=l2; ListNode temp3=sentinel; while(temp1!=null || temp2!=null){ sum/=10; if(temp1!=null){ sum+=temp1.val; temp1=temp1.next; } if(temp2!=null){ sum+=temp2.val; temp2=temp2.next; } temp3.next=new ListNode(sum%10); temp3=temp3.next; } if(sum/10!=0) temp3.next=new ListNode(sum/10); return sentinel.next; } }
Discussion
这题并不难,但是在细节的处理上还是要花点心思的。1. sentinel的妙用
本题如果不用sentinel会有最后多出一个Node的问题。需要用if语句控制最后一个Node的生成。但是,如果用sentinel,需要的时候才会生成新的Node,不需要就不生成了,所以最后不会出现多出一个Node的情况。
2. sum的妙用
如果不用sum,直接用temp1.val + temp2.val + carry的话,则需要讨论temp1跟temp2是否为空指针的情况,代码上不简洁。
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