permutations

Permutations.java

/**
 * Write a description of class Permutations here.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class Permutations
{
    // instance variables - replace the example below with your own
    public static int[] chain(int[] p1, int[] p2) {
        int[] result = new int[p1.length];
        for (int i=0; i < result.length; i++) {
            result[i] = p1[p2[i]];
        }
        return result;
    }

    public static int[] inverse(int[] perm) {
        int[] result = new int[perm.length];
        int[] arr = new int[perm.length];
        for (int i=0; i < result.length; i++) {
            result[perm[i]] = i;
        }
        return result;
    }

    public static int[] square(int[] perm) {
        return chain(perm , perm);
    }

    public static int[] power(int[] perm, int k) {
        while (k != 1 && k != -1 && k !=0) {
            if ( k % 2 == 0) {
                return chain(power(perm, k/2), power(perm, k/2));
            } else {
                return chain(power(perm, (k+1)/2), power(perm, (k-1)/2));
            }
        }
        if (k==0 || k== -1) {
            return inverse(perm);
        }
        return perm;
    }
}