225. Implement Stack using Queues

/*
// Implement the following operations of a stack using queues.

// push(x) -- Push element x onto stack.
// pop() -- Removes the element on top of the stack.
// top() -- Get the top element.
// empty() -- Return whether the stack is empty.
*/

class MyStack {

    private Queue<Integer> value = new LinkedList<>();
    private Queue<Integer> temp = new LinkedList<>();
    private int top;
    
    /** Initialize your data structure here. */
    public MyStack() {
        
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        value.add(x);
        top = x;
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        while (value.size() > 1) {
            top = value.remove();
            temp.add(top);
        }
        
        int element = value.remove();
        
        while (temp.size() > 0) {
            top = temp.remove();
            value.add(top);
        }
        
        return element;
    }
    
    /** Get the top element. */
    public int top() {
        return top;
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return value.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */