_225.java

package com.fishercoder.solutions;

import java.util.LinkedList;
import java.util.Queue;
/**
 * 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.

 Notes:
 You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
 Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
 You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
 Update (2015-06-11):
 The class name of the Java function had been updated to MyStack instead of Stack.*/

public class _225 {

    public static class Solution1 {
        class MyStack {

            Queue<Integer> q = new LinkedList();

            // Push element x onto stack.
            public void push(int x) {
                q.offer(x);
                for (int i = 1; i < q.size(); i++) {
                    q.offer(q.remove());
                }
            }

            // Removes the element on top of the stack.
            public void pop() {
                q.poll();
            }

            // Get the top element.
            public int top() {
                return q.peek();
            }

            // Return whether the stack is empty.
            public boolean empty() {
                return q.isEmpty();
            }
        }
    }
}