leetcode_18.cpp

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int>> res;
        sort(nums.begin(), nums.end());

        for(int i = 0; i < nums.size(); i++){
            if (i > 0 && nums[i] == nums[i - 1]) continue;
            for(int j = i+1; j < nums.size(); j++){
                if (j > i + 1 && nums[j] == nums[j - 1]) continue;
                int left = j + 1, right = nums.size() - 1;
                long long value = (long long)target - nums[i] - nums[j];
                while(left < right){
                    int sum  = nums[left] + nums[right];
                    if(sum == value){
                        res.push_back({nums[i], nums[j], nums[left], nums[right]});
                        while (left < right && nums[left] == nums[left + 1]) left++;
                        while (left < right && nums[right] == nums[right - 1]) right--;
                        left++;
                        right--;
                    }
                    else if(sum < value) left++;
                    else right--;
                }
            }
        }
        return res;
    }
};