225. Implement Stack using Queues

Problem

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.

Example:


MyStack stack = new MyStack();

stack.push(1);
stack.push(2);  
stack.top();   // returns 2
stack.pop();   // returns 2
stack.empty(); // returns false

Note:

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).

Problem Summary

The problem requires implementing the basic operations of a stack using queues: push(x), pop(), top(), empty().

Solution Approach

Implement according to the problem requirements.

Code


package leetcode

type MyStack struct {
	enque []int
	deque []int
}

/** Initialize your data structure here. */
func Constructor225() MyStack {
	return MyStack{[]int{}, []int{}}
}

/** Push element x onto stack. */
func (this *MyStack) Push(x int) {
	this.enque = append(this.enque, x)
}

/** Removes the element on top of the stack and returns that element. */
func (this *MyStack) Pop() int {
	length := len(this.enque)
	for i := 0; i < length-1; i++ {
		this.deque = append(this.deque, this.enque[0])
		this.enque = this.enque[1:]
	}
	topEle := this.enque[0]
	this.enque = this.deque
	this.deque = nil

	return topEle
}

/** Get the top element. */
func (this *MyStack) Top() int {
	topEle := this.Pop()
	this.enque = append(this.enque, topEle)

	return topEle
}

/** Returns whether the stack is empty. */
func (this *MyStack) Empty() bool {
	if len(this.enque) == 0 {
		return true
	}

	return false
}