225.用队列实现栈

两天宇宙人

2020-02-16

😝实现

class MyStack {
public:
    /** Initialize your data structure here. */
    MyStack() {
        
    }
    
    /** Push element x onto stack. */
    void push(int x) {
        q.push(x);
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() {
        int val;
        while(q.size() != 1) {
            int x = q.front();
            h.push(x);
            q.pop();
        }
        val = q.front();
        // h.push(x);
        q.pop();
        while(h.size()) {
            int x = h.front();
            h.pop();
            q.push(x);
        }
        return val;
    }
    
    /** Get the top element. */
    int top() {
        int val;
        while(q.size() != 1) {
            int x = q.front();
            h.push(x);
            q.pop();
        }
        val = q.front();
        h.push(val);
        q.pop();
        while(h.size()) {
            int x = h.front();
            h.pop();
            q.push(x);
        }
        return val;
    }
    
    /** Returns whether the stack is empty. */
    bool empty() {
        return q.size() == 0;
    }
private:
    queue<int> q, h;
};