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implementQueueUsingStacks.js
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56 lines (49 loc) · 1.57 KB
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/**
* LeetCode 232. Implement Queue using Stacks
* https://leetcode.com/problems/implement-queue-using-stacks/
*
* Implement a first in first out (FIFO) queue using only two stacks.
* The implemented queue should support all the functions of a normal queue
* (push, peek, pop, and empty).
*
* Implement the MyQueue class:
* - void push(int x) — Pushes element x to the back of the queue.
* - int pop() — Removes the element from the front of the queue and returns it.
* - int peek() — Returns the element at the front of the queue.
* - boolean empty() — Returns true if the queue is empty, false otherwise.
*
* Notes:
* - You must use only standard operations of a stack, which means only
* push to top, peek/pop from top, size, and is empty operations are valid.
*
* Constraints:
* - 1 <= x <= 9
* - At most 100 calls will be made to push, pop, peek, and empty.
* - All the calls to pop and peek are valid.
*/
const MyQueue = function () {
this.stack1 = [];
this.stack2 = [];
};
MyQueue.prototype.push = function (item) {
this.stack1.push(item);
};
MyQueue.prototype.pop = function () {
this.prepareOutput();
return this.stack2.pop();
};
MyQueue.prototype.peek = function () {
this.prepareOutput();
return this.stack2[this.stack2.length - 1];
};
MyQueue.prototype.empty = function () {
return this.stack1.length === 0 && this.stack2.length === 0;
};
MyQueue.prototype.prepareOutput = function () {
if (this.stack2.length === 0) {
while (this.stack1.length > 0) {
this.stack2.push(this.stack1.pop());
}
}
};
module.exports = { MyQueue };