implement-stack-using-queues.js

// 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.
//
//
// Credits:Special thanks to @jianchao.li.fighter for adding this problem and all test cases.


/**
 * @constructor
 */
var Stack = function() {
    this.arr = [];
};

/**
 * @param {number} x
 * @returns {void}
 */
Stack.prototype.push = function(x) {
    this.arr.push(x);
};

/**
 * @returns {void}
 */
Stack.prototype.pop = function() {
    this.arr.pop();
};

/**
 * @returns {number}
 */
Stack.prototype.top = function() {
    return this.arr[this.arr.length - 1];
};

/**
 * @returns {boolean}
 */
Stack.prototype.empty = function() {
    return this.arr.length === 0;
};