232. Implement Queue using Stacks

⭐️

# 題目敘述

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

# 解題思路

# Solution

import java.util.ArrayList;

class MyQueue {

    private int front;

    private int rear;

    private ArrayList<Integer> queue = new ArrayList<>();

    public MyQueue() {

        this.front = 0;

        this.rear = 0;

    }

    public int getFront() {

        return this.front;

    }

    public int getRear() {

        return this.rear;

    }

    public void setFront(int f) {

        this.front = f;

    }

    public void setRear(int r) {

        this.rear = r;

    }

    public void push(int x) {

        queue.add(x);

        setRear(getRear() + 1);

    }

    public int pop() {

        int temp = queue.get(0);

        queue.remove(0);

        setFront(getFront() + 1);

        return temp;

    }

    public int peek() {

        int temp = queue.get(0);

        return temp;

    }

    public boolean empty() {

        return getFront() == getRear();

    }

}

/**

 * 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();

 */

#include <vector>

using namespace std;

class MyQueue {

 private:

  int front;

  int rear;

  vector<int> queue;

 public:

  MyQueue() {

    this->front = 0;

    this->rear = 0;

  }

  int getFront() { return this->front; }

  int getRear() { return this->rear; }

  void setFront(int f) { this->front = f; }

  void setRear(int r) { this->rear = r; }

  void push(int x) {

    queue.push_back(x);

    setRear(getRear() + 1);

  }

  int pop() {

    int tmp = queue[getFront()];

    setFront(getFront() + 1);

    return tmp;

  }

  int peek() {

    int tmp = queue[getFront()];

    return tmp;

  }

  bool empty() {

    return getFront() == getRear();

  }

};

/**

 * 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();

 */