g0201_0300.s0225_implement_stack_using_queues

Class MyStack

java.lang.Object

g0201_0300.s0225_implement_stack_using_queues.MyStack

public class MyStack
extends Object

225 - Implement Stack using Queues.

Easy

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).

Implement the MyStack class:

• void push(int x) Pushes element x to the top of the stack.
• int pop() Removes the element on the top of the stack and returns it.
• int top() Returns the element on the top of the stack.
• boolean empty() Returns true if the stack is empty, false otherwise.

Notes:

• You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
• Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue’s standard operations.

Example 1:

Input [“MyStack”, “push”, “push”, “top”, “pop”, “empty”] [ [], [1], [2], [], [], []]

Output: [null, null, null, 2, 2, false]

Explanation:

MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False 

Constraints:

• 1 <= x <= 9
• At most 100 calls will be made to push, pop, top, and empty.
• All the calls to pop and top are valid.

Follow-up: Can you implement the stack using only one queue?

Constructor Summary

Constructors

Constructor and Description
MyStack()

Method Summary

Modifier and Type	Method and Description
boolean	empty()
int	pop()
void	push(int x)
int	top()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MyStack

public MyStack()

Method Detail

push

public void push(int x)

pop

public int pop()

top

public int top()

empty

public boolean empty()