﻿ Java exercises: Create all possible permutations of a given array of distinct integers - w3resource # Java Array Exercises: Create all possible permutations of a given array of distinct integers

## Java Array: Exercise-68 with Solution

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 java.util.*;
import java.util.List;

public class solution {
public static void main(String[] args) throws Exception {
int[] nums1 = {1, 2, 3, 4};
System.out.println("\nOriginal array: "+Arrays.toString(nums1));
List<List<Integer>> result1 = new solution().permute(nums1);
System.out.println("\nPossible permutations of the said array:");
result1.forEach(System.out::println);
int[] nums2 = {1, 2, 3};
System.out.println("\nOriginal array: "+Arrays.toString(nums2));
List<List<Integer>> result2 = new solution().permute(nums2);
System.out.println("\nPossible permutations of the said array:");
result2.forEach(System.out::println);
}

public List<List<Integer>> permute(int[] nums) {
List<List<Integer>> result = new ArrayList<>();
Permutation(0, nums, result);
return result;
}

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);
} 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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## Java: Tips of the Day

Array vs ArrayLists:

The main difference between these two is that an Array is of fixed size so once you have created an Array you cannot change it but the ArrayList is not of fixed size. You can create instances of ArrayLists without specifying its size. So if you create such instances of an ArrayList without specifying its size Java will create an instance of an ArrayList of default size.

Once an ArrayList is full it re-sizes itself. In fact, an ArrayList is internally supported by an array. So when an ArrayList is resized it will slow down its performance a bit as the contents of the old Array must be copied to a new Array.

At the same time, it's compulsory to specify the size of an Array directly or indirectly while creating it. And also Arrays can store both primitives and objects while ArrayLists only can store objects.

Ref: https://bit.ly/3o8L2KH