【一刷《剑指Offer》】面试题 7：用两个栈实现队列

class MyQueue {
public:
    stack<int> inStack;
    stack<int> outStack;
    MyQueue() {}
    
    void push(int x) {
        inStack.push(x);
    }
    
    int pop() {
        if(outStack.empty())
        {
            if(inStack.empty())
                return -1;
            while(!inStack.empty())
            {
                int tmp=inStack.top();
                inStack.pop();
                outStack.push(tmp);
            }
        }
        int dele=outStack.top();
        outStack.pop();
        return dele;
    }
    
    int peek() {
        int res=this->pop();
        outStack.push(res);
        return res;
    }
    
    bool empty() {
        return inStack.empty() && outStack.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();
 */

class MyStack {
public:
    queue<int> q1;
    queue<int> q2;
    MyStack() {}
    
    void push(int x) {
        q1.push(x);
    }
    
    int pop() {
        int n=q1.size();
        n--;
        while(n--)
        {
            q2.push(q1.front());
            q1.pop();
        }
        int res=q1.front();
        q1.pop();
        q1 = q2;
        while (!q2.empty())
            q2.pop();
        return res;
    }
    
    int top() {
        return q1.back();
    }
    
    bool empty() {
        return q1.empty() && q2.empty();
    }
};
 
/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack* obj = new MyStack();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->top();
 * bool param_4 = obj->empty();
 */