# 4SUM leetcode Solution - Correct, Optimal and Working

``````class Solution {
public:
vector<vector<int> > fourSum(vector<int> &num, int target) {

set< vector<int> >s;

int n = num.size();

vector<int> temp;
vector< vector<int> > ans;

sort(num.begin(), num.end());

for(int i = 0 ; i < (n - 3) ; i++ ) {

for( int j = i+1 ; j < n-2 ; j++ ) {

int k = j + 1, l = n - 1;

while ( k < l ) {

int sum = num[i] + num[j] + num[k] + num[l];

if( sum == target ) {
temp.clear();
temp.push_back(num[i]);
temp.push_back(num[j]);
temp.push_back(num[k]);
temp.push_back(num[l]);
s.insert(temp);

k++;
l--;

while( k < l && num[l] == num[l+1]) {
l--;
}

while(k < l && num[k] == num[k-1] ) {
k++;
}

}
else if( sum < target ) {
k++;
}
else {
l--;
}
}
}
}

/*for( int i = ans.size() - 1 ; i >= 0 ; i-- ) {

for( int j = i - 1 ; j >= 0 ; j-- ) {

if( ans[i][0] == ans[j][0] && ans[i][1] == ans[j][1] && ans[i][2] == ans[j][2] ) {
ans.erase(ans.begin() + j);
}
}
}*/

for( set< vector<int> >::iterator itr = s.begin() ; itr != s.end() ; itr++ ) {
ans.push_back(*itr);
}

return ans;

}
};
``````