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package g0201_0300.s0232_implement_queue_using_stacks;

// #Easy #Stack #Design #Queue #Data_Structure_I_Day_9_Stack_Queue
// #Programming_Skills_I_Day_11_Containers_and_Libraries #Level_2_Day_16_Design
// #2022_07_04_Time_1_ms_(67.21%)_Space_41.8_MB_(58.63%)

import java.util.ArrayDeque;
import java.util.Deque;

/**
 * 232 - Implement Queue using Stacks\.
 *
 * Easy
 *
 * 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.
 * *   Depending on your language, the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations.
 *
 * **Example 1:**
 *
 * **Input:**
 *
 *     ["MyQueue", "push", "push", "peek", "pop", "empty"]
 *     [ [], [1], [2], [], [], []]
 *
 * **Output:**
 *
 *     [null, null, null, 1, 1, false]
 *
 * **Explanation:**
 *
 *     MyQueue myQueue = new MyQueue();
 *     myQueue.push(1); // queue is: [1]
 *     myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)
 *     myQueue.peek(); // return 1
 *     myQueue.pop(); // return 1, queue is [2]
 *     myQueue.empty(); // return false 
 *
 * **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.
 *
 * **Follow-up:** Can you implement the queue such that each operation is **[amortized](https://en.wikipedia.org/wiki/Amortized_analysis)** `O(1)` time complexity? In other words, performing `n` operations will take overall `O(n)` time even if one of those operations may take longer.
**/
public class MyQueue {
    private Deque left;
    private Deque right;
    // Initialize your data structure here.
    public MyQueue() {
        left = new ArrayDeque<>();
        right = new ArrayDeque<>();
    }

    // Push element x to the back of queue.
    public void push(int x) {
        while (!right.isEmpty()) {
            left.add(right.pop());
        }
        left.add(x);
    }

    // Removes the element from in front of queue and returns that element.
    public int pop() {
        while (!left.isEmpty()) {
            right.add(left.pop());
        }
        return right.pop();
    }

    // Get the front element.
    public int peek() {
        while (!left.isEmpty()) {
            right.add(left.pop());
        }
        return right.peek();
    }

    // Returns whether the queue is empty.
    public boolean empty() {
        return right.isEmpty() && left.isEmpty();
    }
}

/*
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue obj = new MyQueue();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.empty();
 */