【Leetcode】232. Using stack to realize queue

subject

Please use only two stacks to implement the FIFO queue . The queue should support all operations supported by the general queue （push、pop、peek、empty）：

Realization MyQueue class ：

• void push(int x) Put the element x Push to the end of the queue
• int pop() Remove from the beginning of the queue and return the element
• int peek() Returns the element at the beginning of the queue
• boolean empty() If the queue is empty , return true ; otherwise , return false

Ideas

• Stack in operation ： Data can be directly put into the input stack
• The stack, : If the output stack is empty , Then directly send all the data in the input stack to the output stack , Then out of the stack , Achieve the goal of first in, first out , If the output stack is not empty , First pop up all the data in the output stack , Then proceed as above
• The stack is empty ： Neither the input stack nor the output stack has data .

Code

class MyQueue {
    
public:
    stack<int> stIn;
    stack<int> stOut;

    MyQueue() {
    

    }
    
    void push(int x) {
    
        stIn.push(x);//  Queue in operation   Just enter the stack directly 
    }
    
    int pop() {
    
        //  First judge whether the output stack is empty 
        if(stOut.empty()){
    
            //  If it's empty   Import all input station data 
            while(!stIn.empty())
            {
    
                stOut.push(stIn.top());//  Import the input stack elements 
                stIn.pop();//  Input stack elements out of stack 
            }
        }
        int result = stOut.top();//  Out of the stack 
        stOut.pop();
        return result;
    }
    
    int peek() {
    
        //  Take the top element of the stack 
        int res = this->pop();
        stOut.push(res);//  because pop Function pops up the element res  Add it back 
        return res;
    }
    
    bool empty() {
    
        return stIn.empty() && stOut.empty();//  Only the input stack and output stack are all empty   It's empty 
    }
};

/** * 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(); */