permutation.java

public class Permutation {

    public static void main(String[] args) {
        int[] arr = { 1, 2, 3 };
        perm(arr, 0);
    }

    public static void perm(int[] arr, int pivot) {
        
        if (pivot == arr.length) { 
            print(arr);
            return;
        }

        for (int i = pivot; i < arr.length; i++) {
            swap(arr, i, pivot);
            perm(arr, pivot + 1);
            swap(arr, i, pivot);
        }

    }

    public static void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }

    public static void print(int[] arr) {

        for (int i = 0; i < arr.length; i++) {
            if (i == arr.length - 1)
                System.out.println(arr[i]);
            else
                System.out.print(arr[i] + ",");
        }
    }
}

StrPermutation.java

public class PermutationString {

	public static void main(String[] args) {
		permutation("abcd");
	}

	public static void permutation(String str) {
		permutation("", str);
	}

	private static void permutation(String prefix, String str) {
		int n = str.length();
		if (n == 0)
			System.out.println(prefix);
		else {
			for (int i = 0; i < n; i++)
				permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i + 1, n));
		}
	}
}