Factorial with stack

factorial

class Frame {
    int number;
    int answer;
    boolean done;

    public Frame(int number, int answer, boolean done){
        this.number = number;
        this.answer = answer;
        this.done = done;
    }
}

public class Solution{
    Stack<Frame> stack = new Stack<>();
    //@param root: The root of binary tree.

    int fact(int n)  {
        stack.push(new Frame(n, 0, false));
        Frame f = stack.peek();
        while(!stack.empty()) {
            if(f.done) {
                System.out.println("Popping " + f.number);
                stack.pop();
                if(!stack.empty()) {
                    stack.peek().answer = f.answer * stack.peek().number;
                    stack.peek().done = true;
                }
            } else {
                int number = f.number;
                if(number == 0) {
                    System.out.println("Return from " + number);
                    stack.peek().answer = 1;
                    stack.peek().done = true;
                } else  {
                    System.out.println("Push " + (number - 1));
                    stack.push(new Frame(number-1, 0, false));
                }
            }
            if (! stack.empty()) {
                f = stack.peek();
            }
        }

        return f.answer;
    }

    public static void main(String[] args)  {
        System.out.println("Result: " + new Solution().fact(10));
    }
}