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.

 

 1 public class Solution {
 2     public ArrayList<ArrayList<Integer>> threeSum(int[] num) {
 3         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
 4         if(num.length<=2) return res;
 5         Arrays.sort(num);
 6         int len = num.length;
 7         for(int i=0;i<len;i++){
 8             int sum = 0-num[i];
 9             int start = i+1;
10             int end = len-1;
11             while(start<end){
12                 if(num[start]+num[end]<sum){
13                     start++;
14                 }
15                 else if(num[start]+num[end]>sum){
16                     end--;
17                 }
18                 else{
19                     ArrayList<Integer> temp = new ArrayList<Integer>();
20                     temp.add(num[i]); temp.add(num[start]); temp.add(num[end]);
21                     res.add(temp);
22                     start++;end--;
23                     while(start<end && num[start-1]==num[start]){
24                         start++;
25                     }
26                     while(start<end && num[end+1]==num[end]){
27                         end--;
28                     }
29                 }
30             }
31             while(i<len-1 &&num[i+1]==num[i]){
32                 i++;
33             }
34         }
35         return res;
36     }
37 }
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posted @ 2014-02-06 05:28  krunning  阅读(117)  评论(0)  编辑  收藏  举报