leetcode-3sum（N^2logN）

題目：
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: 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]
]
求解：

    class Solution {
        public:
        bool midFind(vector<int>& v , int  s, int e , int data){
            int m = -1 ;;
            while( s <= e){
                m = s +  (( e - s ) >> 1 );
                if(v[m] == data){
                    return true;
                }
                else if(data < v[m]){
                    e = m - 1 ;
                }
                else{
                    s = m + 1 ;
                }
            }
            return false;
        }
        vector<vector<int>> threeSum(vector<int>& nums) {
            vector<vector<int>> res;
            sort(nums.begin(),nums.end());
            int len = nums.size();
            for(int i = 0 ; i < len ; i++){
                if(i != 0 && nums[i] == nums[i-1]){
                        continue;
                }
                for(int  j = i + 1;  j < len - 1;j++){
                    if(j != i + 1 && nums[j] == nums[j-1]){
                        continue;
                    }
                    int search = -(nums[i] + nums[j]);
                    if(midFind(nums , j+1 , len -1 ,  search)){
                        vector<int> tmp ;
                        tmp.push_back(nums[i]);
                        tmp.push_back(nums[j]);
                        tmp.push_back(search);
                        res.push_back(tmp);
                    }
                }
            }
            return res;
        }   
    };