【队栈】leetcode_232_用栈实现队列

【队栈】leetcode_232_用栈实现队列

c++

class MyQueue {
public:
    stack<int> s_in;
    stack<int> s_out;
    /** Initialize your data structure here. */
    MyQueue() {
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        s_in.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        if (!s_out.empty()){
                int tmp = s_out.top();
                s_out.pop();
            return tmp;
        }else{
            while(!s_in.empty()){
                s_out.push(s_in.top());
                s_in.pop();
            }
        }
        int tmp = s_out.top();
        s_out.pop();
        return tmp;
        // if(s_out.empty()){
        //     while(!s_in.empty()){
        //         int tmp = s_in.top();
        //         s_in.pop();
        //         s_out.push(tmp);
        //     }
        // }
        // int tmp = s_out.top();
        // s_out.pop();
        // return tmp;
    }
    
    /** Get the front element. */
    int peek() {
        int tmp = this->pop();
        s_out.push(tmp);
        return tmp;
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        if(s_out.empty() && s_in.empty()){
            return true;
        }else{
            return false;
        }

    }
};

/**
 * 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();
 */