[LeetCode] 4sum

class Solution {
public:
    vector<vector<int> > fourSum(vector<int> &num, int target) {
         sort(num.begin(),num.end());
         vector<vector<int> > res;
         int* a = &num[0];
         int len = num.size();
         for (int i = 0; i < len; i++) {
             if (i > 0 && num[i] == num[i-1]) continue;
             for (int j = i+1; j < len; j++) {
                 if (j > i+1 && num[j] == num[j-1]) continue;
                 int x = j+1, y = len - 1;
                 while (x < y) {
                     int t = a[i] + a[j] + a[x] + a[y];
                     if (t == target) {
                         res.push_back({a[i], a[j], a[x], a[y]});
                         while (x < y && a[x+1] == a[x]) x++;
                         while (x < y && a[y-1] == a[y]) y--;
                         x++; y--;
                     } else if (t > target) {
                         y--;
                     } else {
                         x++;
                     }
                 }
             }
         }
         return res;
    }
};