3sum

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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)

同样也是修改了一遍就通过了。做多了就会越来越熟练。

求三个数字之和等于0.要求输出的数字队列用升序排列。

我直接用暴力法，也就是三个for循环来完成。

想想看有哪里可以优化的呢？

上代码

public class Solution {    public List<List<Integer>> threeSum(int[] num) {Arrays.sort(num);List<List<Integer>> rstList=new ArrayList<List<Integer>>();for(int index1=0;index1<num.length;++index1){if(index1!=0&&num[index1]==num[index1-1])continue;for(int index2=index1+1;index2<num.length;++index2){if(index2!=index1+1&&num[index2]==num[index2-1])continue;for(int index3=index2+1;index3<num.length;++index3){if(index3!=index2+1&&num[index3]==num[index3-1])continue;if(num[index1]+num[index2]+num[index3]==0){List<Integer> tmp=new ArrayList<>();tmp.add(num[index1]);tmp.add(num[index2]);tmp.add(num[index3]);rstList.add(tmp);}}}}    return rstList;            }}

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