leetcode@ [18]4Sum

struct quadruplet{
    int a,b,c,d;
    quadruplet() {}
    quadruplet(int aa,int bb,int cc,int dd){
        this->a=aa; this->b=bb; this->c=cc; this->d=dd;
    }
    bool operator<(const quadruplet& t)const{
        if((a-t.a<0)||(a==t.a&&b<t.b)||(a==t.a&&b==t.b&&c<t.c)||(a==t.a&&b==t.b&&c==t.c&&d<t.d)) return true;
        return false;    
    }
};
class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        
        vector<vector<int> > ans; ans.clear();
        if(nums.size()<=3) return ans;
        
        int cntAns=0;
        vector<int> tmp(4);  tmp.clear();
        set<quadruplet> st; st.clear();
        
        int left,right,sum;
        
        for(int i=0;i<=nums.size()-4;i++){
            for(int j=i+1;j<=nums.size()-3;j++){
                left=j+1;
                right=nums.size()-1;
                while(left<right){
                    sum=nums[i]+nums[j]+nums[left]+nums[right];
                    if(sum==target){
                        tmp.push_back(nums[i]); tmp.push_back(nums[j]);
                        tmp.push_back(nums[left]); tmp.push_back(nums[right]);
                        sort(tmp.begin(),tmp.end());
                        
                        quadruplet quad=quadruplet(tmp[0],tmp[1],tmp[2],tmp[3]);
                        if(!st.count(quad)){
                            st.insert(quad);
                            ans.resize(++cntAns);
                            ans[cntAns-1]=tmp;
                        }
                        tmp.clear();
                        
                        right--; left++;
                    }
                    else if(sum>target) right--;
                    else left++;
                }
            }    
        }

        
        return ans;        
    }
};