1 struct quadruplet{
2 int a,b,c,d;
3 quadruplet() {}
4 quadruplet(int aa,int bb,int cc,int dd){
5 this->a=aa; this->b=bb; this->c=cc; this->d=dd;
6 }
7 bool operator<(const quadruplet& t)const{
8 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;
9 return false;
10 }
11 };
12 class Solution {
13 public:
14 vector<vector<int>> fourSum(vector<int>& nums, int target) {
15 sort(nums.begin(),nums.end());
16
17 vector<vector<int> > ans; ans.clear();
18 if(nums.size()<=3) return ans;
19
20 int cntAns=0;
21 vector<int> tmp(4); tmp.clear();
22 set<quadruplet> st; st.clear();
23
24 int left,right,sum;
25
26 for(int i=0;i<=nums.size()-4;i++){
27 for(int j=i+1;j<=nums.size()-3;j++){
28 left=j+1;
29 right=nums.size()-1;
30 while(left<right){
31 sum=nums[i]+nums[j]+nums[left]+nums[right];
32 if(sum==target){
33 tmp.push_back(nums[i]); tmp.push_back(nums[j]);
34 tmp.push_back(nums[left]); tmp.push_back(nums[right]);
35 sort(tmp.begin(),tmp.end());
36
37 quadruplet quad=quadruplet(tmp[0],tmp[1],tmp[2],tmp[3]);
38 if(!st.count(quad)){
39 st.insert(quad);
40 ans.resize(++cntAns);
41 ans[cntAns-1]=tmp;
42 }
43 tmp.clear();
44
45 right--; left++;
46 }
47 else if(sum>target) right--;
48 else left++;
49 }
50 }
51 }
52
53
54 return ans;
55 }
56 };
