Leetcode 225 - Implement stack using queues

Note:

  • Because we are using queues, we can only use push and shift (To get the first element).
  • DO NOT use pop.
  • One queue is enough for implementation.

Question:
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:

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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

Code:

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var MyStack = function() {
this.queue = [];
};

/**
* @param {number} x
* @return {void}
*/
MyStack.prototype.push = function(x) {
this.queue.push(x);
};

/**
* @return {number}
*/
MyStack.prototype.pop = function() {
let length = this.queue.length;
while(length-- > 1) {
this.push(this.queue.shift());
}
return this.queue.shift();
};

/**
* @return {number}
*/
MyStack.prototype.top = function() {
const res = this.pop();
this.push(res);
return res;
};

/**
* @return {boolean}
*/
MyStack.prototype.empty = function() {
return !this.queue.length;
};

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