Java: Create all possible permutations of a given array of distinct integers

Last update on December 21 2024 09:33:33 (UTC/GMT +8 hours)

Write a Java program to create all possible permutations of a given array of distinct integers.

Example:
Input :
nums1 = {1, 2, 3, 4}
nums2 = {1, 2, 3}
Output:
Possible permutations of the said array:
[1, 2, 3, 4]
[1, 2, 4, 3]
[1, 3, 2, 4]
[1, 3, 4, 2]
....
[4, 3, 2, 1]
[4, 3, 1, 2]
[4, 1, 3, 2]
[4, 1, 2, 3]
Possible permutations of the said array:
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 2, 1]
[3, 1, 2]

Sample Solution:

Java Code:

// Import the necessary Java classes.
import java.util.*;
import java.util.List;

// Define the 'solution' class.
public class solution {
    // Main method to demonstrate permutation of arrays.
    public static void main(String[] args) throws Exception {
        // Initialize the first array.
        int[] nums1 = {1, 2, 3, 4};
        System.out.println("\nOriginal array 1: " + Arrays.toString(nums1));
        // Calculate and display the permutations of the first array.
        List<List<Integer>> result1 = new solution().permute(nums1);
        System.out.println("\nPossible permutations of the first array:");
        result1.forEach(System.out::println);

        // Initialize the second array.
        int[] nums2 = {1, 2, 3};
        System.out.println("\nOriginal array 2: " + Arrays.toString(nums2));
        // Calculate and display the permutations of the second array.
        List<List<Integer>> result2 = new solution().permute(nums2);
        System.out.println("\nPossible permutations of the second array:");
        result2.forEach(System.out::println);
    }

    // Method to calculate permutations of an array.
    public List<List<Integer>>permute(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        Permutation(0, nums, result);
        return result;
    }

    // Recursive method to generate permutations.
    private void Permutation(int i, int[] nums, List<List<Integer>> result) {
        if (i == nums.length - 1) {
            List<Integer> list = new ArrayList<>();
            for (int n : nums) list.add(n);
            result.add(list);
        } else {
            for (int j = i, l = nums.length; j < l; j++) {
                int temp = nums[j];
                nums[j] = nums[i];
                nums[i] = temp;
                Permutation(i + 1, nums, result);
                temp = nums[j];
                nums[j] = nums[i];
                nums[i] = temp;
            }
        }
    }
} 

Sample Output:

Original array: [1, 2, 3, 4]

Possible permutations of the said array:
[1, 2, 3, 4]
[1, 2, 4, 3]
[1, 3, 2, 4]
[1, 3, 4, 2]
[1, 4, 3, 2]
[1, 4, 2, 3]
[2, 1, 3, 4]
[2, 1, 4, 3]
[2, 3, 1, 4]
[2, 3, 4, 1]
[2, 4, 3, 1]
[2, 4, 1, 3]
[3, 2, 1, 4]
[3, 2, 4, 1]
[3, 1, 2, 4]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 2, 3, 1]
[4, 2, 1, 3]
[4, 3, 2, 1]
[4, 3, 1, 2]
[4, 1, 3, 2]
[4, 1, 2, 3]

Original array: [1, 2, 3]

Possible permutations of the said array:
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 2, 1]
[3, 1, 2]

Flowchart:

Java Code Editor:

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