232.用栈实现队列

两天宇宙人

2020-02-16

😝实现

class MyQueue {
public:
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        stk.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        while(stk.size() != 1) {
            int x = stk.top();
            stk.pop();
            helper.push(x);
        }
        int x = stk.top();
        stk.pop();
        while(helper.size())
        {
            int x = helper.top();
            helper.pop();
            stk.push(x);
        }
        return x;
    }
    
    /** Get the front element. */
    int peek() {
        while(stk.size() != 1) {
            int x = stk.top();
            stk.pop();
            helper.push(x);
        }
        int x = stk.top();
        while(helper.size())
        {
            int x = helper.top();
            helper.pop();
            stk.push(x);
        }
        return x;
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return stk.size() == 0;
    }
private:
    stack<int > stk, helper;
};