sum_4.java

import java.util.*;

public class sum_4 {

    public static List<List<Integer>> fourSum(int[] nums, int target) {
        int n = nums.length;
        Set<List<Integer>> set = new HashSet<>();

        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                for (int k = j + 1; k < n; k++) {
                    for (int l = k + 1; l < n; l++) {
                        long sum = (long)nums[i] + nums[j];
                        sum += nums[k];
                        sum += nums[l];

                        if (sum == target) {
                            List<Integer> temp = Arrays.asList(nums[i], nums[j], nums[k], nums[l]);
                            Collections.sort(temp);
                            set.add(temp);
                        }
                    }
                }
            }
        }
        List<List<Integer>> ans = new ArrayList<>(set);
        return ans;
    }

    public static void main(String[] args) {
        int[] nums = {4, 3, 3, 4, 4, 2, 1, 2, 1, 1};
        int target = 9;
        List<List<Integer>> ans = fourSum(nums, target);
        System.out.println("The quadruplets are: ");
        for (List<Integer> it : ans) {
            System.out.print("[");
            for (int ele : it) {
                System.out.print(ele + " ");
            }
            System.out.print("] ");
        }
        System.out.println();
    }
}