Divide 1 to n into two groups with minimum sum difference

import java.util.HashSet;
import java.util.Set;

public class SubsetDifference {
    public static int[][] minSubsetDiff(int n) {
        int S = n * (n + 1) / 2;
        int target = S / 2;
        boolean[] dp = new boolean[target + 1];
        int[][] subset = new int[target + 1][];
        dp[0] = true;

        // Find all possible subset sums and store
        for (int i = 1; i <= n; i++) {
            for (int j = target; j >= i; j--) {
                if (dp[j - i]) {
                    dp[j] = true;
                    subset[j] = new int[subset[j - i].length + 1];
                    System.arraycopy(subset[j - i], 0, subset[j], 0, subset[j - i].length);
                    subset[j][subset[j - i].length] = i;
                }
            }
        }

        // Find the subset closest (smaller or equal) 
        // to target
        int s1 = 0;
        for (int i = target; i >= 0; i--) {
            if (dp[i]) {
                s1 = i;
                break;
            }
        }

        int[] subset1 = subset[s1];
        Set<Integer> set1 = new HashSet<>();
        for (int num : subset1) {
            set1.add(num);
        }
        int[] subset2 = new int[n - subset1.length];
        int index = 0;

        for (int i = 1; i <= n; i++) {
            if (!set1.contains(i)) subset2[index++] = i;
        }

        return new int[][]{subset1, subset2};
    }

    public static void main(String[] args) {
        int n = 4;
        int[][] res = minSubsetDiff(n);

        System.out.print("Subset 1: ");
        for (int x : res[0]) System.out.print(x + " ");
        System.out.println();
        System.out.print("Subset 2: ");
        for (int x : res[1]) System.out.print(x + " ");
        System.out.println();
    }
}

// Function to divide the elements from 1
// to n in two groups with minimum difference
import java.util.*;

class GfG {

    // Function to divide the elements from 1
    // to n in two groups with minimum difference
    static int[][] findGroup(int n) {
        // to store the two groups
        ArrayList<Integer> group1 = new ArrayList<>();
        ArrayList<Integer> group2 = new ArrayList<>();
        
        // to store the sum of both groups
        int sum1 = 0, sum2 = 0;
        
        // find half of sum of elements from 1 to n
        int half = n * (n + 1) / 4;
        
        for (int i = n; i >= 1; i--) {
            // if adding the current element to first
            // group doesn't exceed half, add it
            if (sum1 + i <= half) {
                group1.add(i);
                sum1 += i;
            }
            // else add it to the second group
            else {
                group2.add(i);
                sum2 += i;
            }
        }
        
        // convert groups to int[] arrays
        int[] arr1 = new int[group1.size()];
        for (int i = 0; i < group1.size(); i++) {
            arr1[i] = group1.get(i);
        }
        int[] arr2 = new int[group2.size()];
        for (int i = 0; i < group2.size(); i++) {
            arr2[i] = group2.get(i);
        }
        
        // create the result 2D array
        int[][] res = new int[2][];
        res[0] = arr1;
        res[1] = arr2;
        
        return res;
    }
    
    public static void main(String[] args) {
        int n = 7;
        int[][] res = findGroup(n);
        for (int i = 0; i < 2; i++) {
            for (int j = 0; j < res[i].length; j++) {
                System.out.print(res[i][j] + " ");
            }
            System.out.println();
        }
    }
}