TopCoder SRM 504 Division 2 - 500 point problem

MathContest.java

import java.util.Stack;

public class MathContest {

    public int countBlack(String ballSequence, int repetitions) {
        String newBallSequence = ballSequence;

        Stack<Integer> stack = new Stack<Integer>();
        for (int i = newBallSequence.length() - 1; i >= 0; i--) {
            if (newBallSequence.charAt(i) == 'B')
                stack.push(1);
            else
                stack.push(-1);
        }

        int black = 0;
        boolean white = false;
        while (stack.size() > 0) {
            int pop = stack.pop();
            if (pop == 1) {
                black++;
                stack = invert(stack);
            } else {
                white = true;
                stack = reorder(stack);
            }
        }
        if (white)
            return black;
        return black * repetitions;
    }

    public Stack<Integer> reorder(Stack<Integer> stack) {
        Stack<Integer> temp = new Stack<Integer>();
        while (stack.size() > 0)
            temp.push(stack.pop());
        return temp;
    }

    public Stack<Integer> invert(Stack<Integer> stack) {
        Stack<Integer> temp = new Stack<Integer>();
        while (stack.size() > 0)
            temp.push(stack.pop());
        while (temp.size() > 0) {
            stack.push(-temp.pop());
        }
        return stack;
    }

}