Java Program to Show the Permutations of an Integer Array

Question

Trying to show the permutations of an int array using recursion, however for some reason it doesn't print anything when I call the function. Is there something in the main function I'm missing?

     public static void Permutation(int[] a, int prefix) {

    int length = a.length;

    if (length == prefix) {

        printArray(a);

    }

    else {

        for (int i = 0; i < prefix; i++) {

            swap(a, prefix, i);

            Permutation(a, prefix + 1);

            swap(a, prefix, i);

        }
    }
}

public static void swap(int[] a, int x, int y) {

    int z = a[x];

    a[x] = a[y];

    a[y] = z;

}

public static void printArray(int[] thing) {

    System.out.println("\n");

    for (int x = 0; x < thing.length; x++)
        System.out.print(thing[x]);

}

public static void main(String[] args) {

    int a[] = { 1, 2, 3 };
            Permutation(a, 0);
    }

Say I have an int array of 1, 2, and 3. The output should be

1 2 3
1 3 2 
2 1 3 
2 3 1
3 1 2 
3 2 1

Answer 1

看看你的for循环并分析程序:)

for (int i = 0; i < prefix; i++)