018. 4Sum.cpp

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(), nums.end());
        vector<vector<int>>res;
        vector<int>path;
        DFS(res, nums, 0, target, 0, 0, path);
        return res;
    }
    
    void DFS(vector<vector<int>>& res, vector<int>& nums, int pos, int target, int count, int sum, vector<int>& path){
        if(count == 4){
            if(sum == target) res.push_back(path);
            return;
        }
        for(int i = pos; i < nums.size(); i++){
            if(i != pos && nums[i] == nums[i - 1]) continue;
            if(sum + nums[i] + (3 - count) * nums[nums.size() - 1] < target) continue;
            if(sum + (4 - count)* nums[i] > target) break;
            path.push_back(nums[i]);
            DFS(res, nums, i + 1, target, count + 1, sum + nums[i], path);
            path.pop_back();
        }
    }
};