3Sum

//solution
//this is solved by myself and the running time is short ,so I doesn't spend
//much time on the Internet to find the faster solution. and the general thought 
//is similar
//
class Solution {
public:
    vector<vector<int> > threeSum(vector<int> &num) {

        vector<int> triple(3);
        vector<vector<int> > matchVector;
        sort(num.begin(),num.end());//

        for(int i= 0; i<num.size(); i++) {
            if(i==0 || num[i]!=num[i-1]) {//make the first elemment of triple is unique
                int firstElement = num[i];
                int begin = i+1; // determine the second element's start point
                int end = num.size()-1;// determint the third element's end point
                while(begin <end) {// 
                    if(num[begin]+num[end] == -firstElement) {
                        triple[0] = firstElement;
                        triple[1] = num[begin];
                        triple[2] = num[end];
                        matchVector.push_back(triple);
                        while(begin<end && num[begin+1] == num[begin])// find the unique second element
                                begin++;
                                begin++;// locate the second element
                        while(begin<end && num[end-1] == num[end]) // find the unique third element
                                end--;
                                end--;// locate the third element
                    }
                    else
                        if(num[begin]+num[end]<-firstElement) {
                           while(begin<end && num[begin+1] == num[begin]) 
                               begin++;
                               begin++;
                        }
                        else  {
                            while(begin<end && num[end-1] == num[end])
                                end--;
                                end--;
                        }
                            
                }
        }
        }
        return matchVector;
    }
};