Question

How to generate all possible permutations of N numbers in Java

Answer 1

public class MyClass {
    public static void printArray(Integer[] arr) {
        for (Integer n : arr) {
            System.out.print(n + " ");
        }
        System.out.println();
    }
    public static void swap(Integer arr[], int i, int j) {
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }
    public static void heapAlgorithmPermutation(Integer[] arr, int len, int constant_len) {
        if (len == 1) {
            printArray(arr);
            return;
        }

        for (int i = 0; i < len; i++) {
            heapAlgorithmPermutation(arr, len - 1, constant_len);
      
            if (len % 2 == 1)
                swap(arr, 0, len - 1);
            else
                swap(arr, i, len - 1);
        }
    }
    public static void main(String args[]) {
        Integer[] arr = {1, 2, 3, 4};

        heapAlgorithmPermutation(arr, arr.length, arr.length);
    }
}
 
 
 
 
/*
run:
 
1 2 3 4 
2 1 3 4 
3 1 2 4 
1 3 2 4 
2 3 1 4 
3 2 1 4 
4 2 3 1 
2 4 3 1 
3 4 2 1 
4 3 2 1 
2 3 4 1 
3 2 4 1 
4 1 3 2 
1 4 3 2 
3 4 1 2 
4 3 1 2 
1 3 4 2 
3 1 4 2 
4 1 2 3 
1 4 2 3 
2 4 1 3 
4 2 1 3 
1 2 4 3 
2 1 4 3 

*/

 

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