Permutation algorithm for array of integers in Java

Question

I have a working example to generate all char permutations in a String as below:

static ArrayList permutations(String s) {
        if (s == nul         


        

Answer 1

/**
 * 
 * @param startIndex is the position of the suffix first element 
 * @param prefix is the prefix of the pattern 
 * @param suffix is the suffix of the pattern, will determine the complexity
 *  permute method.
 *
 * 
 * The block if (suffix.length == 1) will print
 * the only possible combination of suffix and return for computing next
 * combination.
 *
 *
 * The part after if (suffix.length == 1) is reached if suffix
 * length is not 1 that is there may be many possible combination of suffix
 * therefore make a newSuffix which will have suffix length
 * (suffix.length - 1) and recursively compute the possible
 * combination of this new suffix and also the original suffix prefix
 * positioned by startIndex will change by increasing its value
 * by one (startIndex + 1) % suffix.length
 * 
 * 
 * T(N) = N * T(N - 1) + N
 *      = N! + N!(1 + 1/N + 1/(N * (N - 1)) + ... + 1/N!)
 *      
 *
 */
public static void permute(int startIndex, int prefix[], int suffix[]) {
    if (suffix.length == 1) {
        for (int i = 0; i < prefix.length; i++) {
            System.out.print(prefix[i] + " ");
            }
        System.out.print(suffix[0]);
        System.out.println(" ");
        return;
    }

    for (int i = 0; i < suffix.length; i++) {
        counter++;
        int newPrefix[] = new int[prefix.length + 1];
        System.arraycopy(prefix, 0, newPrefix, 0, prefix.length);
        newPrefix[prefix.length] = suffix[startIndex];
        int newSuffix[] = new int[suffix.length - 1];
        for (int j = 1; j < suffix.length; j++) {
            newSuffix[j - 1] = suffix[(startIndex + j) % suffix.length];
        }
        permute((startIndex % newSuffix.length), newPrefix, newSuffix);
        startIndex = (startIndex + 1) % suffix.length;
    }
}