代码随想录算法训练营第十天｜LeetCode225. 用队列实现栈、232.用栈实现队列

232.用栈实现队列

力扣题目链接

class MyQueue {

stack<int> stackIn;
stack<int> stackOut;

public:
    MyQueue() {
    }
    
    void push(int x) {
        stackIn.push(x);
    }
    
    int pop() {
        if (stackOut.empty()) {
            // 从stIn导入数据直到stIn为空
            while(!stackIn.empty()) {
                stackOut.push(stackIn.top());
                stackIn.pop();
            }
        }
        int result = stackOut.top();
        stackOut.pop();
        return result;
    }
    
    int peek() {
        int res = this->pop(); // 直接使用已有的pop函数
        stackOut.push(res); // 因为pop函数弹出了元素res，所以再添加回去
        return res;
    }
    
    bool empty() {
        return stackIn.empty() && stackOut.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();
 */

225. 用队列实现栈

力扣题目链接

class MyStack {

queue<int> Queue1;
queue<int> Queue2;

public:
    MyStack() {
    }
    
    void push(int x) {
        Queue1.push(x);
    }
    
    int pop() {
        int size = Queue1.size();
        size--;
        while (size--) { // 将que1 导入que2，但要留下最后一个元素
            Queue2.push(Queue1.front());
            Queue1.pop();
        }

        int result = Queue1.front(); // 留下的最后一个元素就是要返回的值
        Queue1.pop();
        Queue1 = Queue2;            // 再将que2赋值给que1
        while (!Queue2.empty()) { // 清空que2
            Queue2.pop();
        }
        return result;
    }
    
    int top() {
        return Queue1.back();
    }
    
    bool empty() {
        return Queue1.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();
 */