【LeetCode从零单排】No15 3Sum

题目

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)

代码

public class Solution {    public List<List<Integer>> threeSum(int[] num) {        Arrays.sort(num);        int a,b,c;        HashSet<List<Integer>> hs=new HashSet();        for(int i=0;i<=num.length-3;i++){            a=num[i];            for(int m=i+1,n=num.length-1; m<n;){                b=num[m];                c=num[n];                if(-a==(b+c)){                    List<Integer> ls=new ArrayList<Integer>();                    ls.add(a);                    ls.add(b);                    ls.add(c);                    hs.add(ls);                    n--;                    m++;                }                else if(-a>(b+c)){                    m++;                }                else{                    n--;                }            }        }        List<List<Integer>> result=new ArrayList(hs);        return result;}    }

代码下载：https://github.com/jimenbian/GarvinLeetCode

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