題目描述

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)

https://www.cnblogs.com/grandyang/p/4481576.html

class Solution {
public:
    vector<vector<int> > threeSum(vector<int> &num) {
        set<vector<int>>res;
        sort(num.begin(),num.end());
        if(num.empty()||num.front()>0||num.back()<0)return {};
        for(int i=0;i<num.size();i++){
            if(num[i]>0)break;
            int t=0-num[i];
            int j=i+1,k=num.size()-1;
            while(j<k){
                if((num[j]+num[k])==t){
                   res.insert({num[i],num[j],num[k]});
                    while(j<k&&num[j]==num[j+1])j++;
                    while(j<k&&num[k]==num[k-1])k--;
                    j++,k--;
                }
                else if((num[j]+num[k])<t)j++;
                else k--;
            }
        }
        return vector<vector<int> >(res.begin(),res.end());
    }
};