#Leetcode# 232. Implement Queue using Stacks

https://leetcode.com/problems/implement-queue-using-stacks/

 

Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

Example:

MyQueue queue = new MyQueue();

queue.push(1);
queue.push(2);  
queue.peek();  // returns 1
queue.pop();   // returns 1
queue.empty(); // returns false

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, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

代码：

class MyQueue {
public:
    /** Initialize your data structure here. */
    MyQueue() {}
    
    /** Push element x to the back of queue. */
    void push(int x) {
        q.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int t = q.front();
        q.pop();
        return t;
    }
    
    /** Get the front element. */
    int peek() {
        if(!q.empty()) return q.front();
        return 0;
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        if(q.size() == 0) return true;
        return false;
    }
    private:
        queue<int> q;
};

/**
 * 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();
 */

　　昨天写过一个这样类似的题目啦