0029_P232_Implement_Queue_using_Stacks.cpp

/* 
Day: 29
Problem Number: 232 (https://leetcode.com/problems/implement-queue-using-stacks)
Date: 29-01-2024 
Description:
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.

Code:  */
class MyQueue {
public:
    MyQueue() {
    }

    void push(int x) {
        stk1.push(x);
    }

    int pop() {
        move();
        int ans = stk2.top();
        stk2.pop();
        return ans;
    }

    int peek() {
        move();
        return stk2.top();
    }

    bool empty() {
        return stk1.empty() && stk2.empty();
    }

private:
    stack<int> stk1;
    stack<int> stk2;

    void move() {
        if (stk2.empty()) {
            while (!stk1.empty()) {
                stk2.push(stk1.top());
                stk1.pop();
            }
        }
    }
};

/**
 * 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();
 * bool param_4 = obj->empty();
 */