leetcode--3Sum

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

• Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
• The solution set must not contain duplicate triplets.

    For example, given array S = {-1 0 1 2 -1 -4},    A solution set is:    (-1, 0, 1)    (-1, -1, 2) 

思路:先确定一个，然后利用Two Sum的做法查找其他两个，注意要查重

[java] view plain copy

1. public class Solution {  
2.     public List<List<Integer>> threeSum(int[] nums) {  
3.         List<List<Integer>> result = new ArrayList<List<Integer>>();  
4.         Arrays.sort(nums);  
5.         int pre = -100000;  
6.         for(int i=0;i<nums.length;i++){  
7.             if(nums[i]!=pre){                 
8.                 int low = i+1;  
9.                 int high = nums.length-1;  
10.                 int pre_in = -100000;  
11.                 while(low<high){                       
12.                     if(nums[low]!=pre_in){                            
13.                         if(nums[low]+nums[high]==-nums[i]){  
14.                             List<Integer> list = new ArrayList<Integer>();   
15.                             list.add(nums[i]);list.add(nums[low]);list.add(nums[high]);  
16.                             result.add(list);  
17.                             pre_in = nums[low];  
18.                             low++;  
19.                             high--;  
20.                         }else if(nums[low]+nums[high]<-nums[i]){  
21.                             low++;  
22.                         }else{  
23.                             high--;  
24.                         }  
25.                     }else{  
26.                         low++;  
27.                     }  
28.                 }     
29.                 pre = nums[i];  
30.             }         
31.         }  
32.       
33.         return result;  
34.     }  
35. }  

原文链接http://blog.csdn.net/crazy__chen/article/details/45506029