package question;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

public class Question18 {
 List<List<Integer>> res = new LinkedList<>();
 List<Integer> list = new LinkedList<>();
 int[] nums;
 int target;
 int k;

 public List<List<Integer>> fourSum(int[] nums, int target) {
 this.nums = nums;
 this.target = target;
 this.k = 4;
 if (nums == null || nums.length < 4) return res;
 Arrays.sort(this.nums);
 huiSu(0, -1);
 return res;
 }

 public boolean huiSu(int sum, int pre) {
 if (list.size() == k) {
 if (sum == target) res.add(new LinkedList<>(list));
 return sum < target;
 }
 for (int i = pre + 1; i + k - list.size() <= nums.length; i++) {
 if (i > pre + 1 && nums[i] == nums[i - 1]) continue;
 list.add(nums[i]);
 boolean flag = huiSu(sum + nums[i], i);
 list.remove(list.size() - 1);
 if (!flag) break;
 }
 return true;
 }
}