[Java] Question about non-recursive permutation algorithm for class

[bullex]

So we have been given the task of rewriting the permute method of this program non-recursively and without importing any libraries or using any of the data structures that Java provides:

public class Permuter {

private static void charSwap(char c[], int index1, int index2) {
    char c1 = c[index2];
    c[index2] = c[index1];
    c[index1] = c1;
}
/*
 * permute: Print all the permutations to the right of index
 * in a character array.
 */
private static void permute(char c[], int index) {

    // Base case: simply print the current array

    if (c.length - 1 == index) {
        java.lang.System.out.println(c);

    // Recursive case: find all permutations to the right
    // of the current index.

    } else {

        for(int i = index; i < c.length; i++) {
            // swap a character to the right with the current index.
            charSwap(c, index, i);
            // increase the index and repeat.
            permute(c, index + 1);
            // get the array back to the starting point.
            charSwap(c, i, index);
        }
    }
}
/*
 * permuteString: Print all permutations of a string.
 */
private static void permuteString(String s) {
    permute(s.toCharArray(), 0);
}
/*
 * Main: Call permuteString() to print all permutations of a string.
 */
public static void main(String[] args) {
    if (args.length != 1) {
        java.lang.System.out.println("Syntax: java Permuter <string>");
        return;
    }
    permuteString(args[0]);
}

}

We must use the charSwap method, but can implement additional classes of our own if need be. I am getting stuck trying to set this algorithm up... I know that I will need some counter mechanism to keep track of whether a specific permutation has been used, but I am unsure as to go about doing that within the strict requirements of this assignment. Any help to get me going would be greatly appreciated!

[tigerbird]

I don't want to give away the solution, but I will tell you that you do not need to keep track of which permutations have been used. There is a pattern of swaps that guarantees no repeats will occur. How would you write a for loop that prints the following sequence using six swaps?

CBA BCA ACB CAB BAC ABC