AcWing 41. 包含min函数的栈

题目链接：https://www.acwing.com/problem/content/description/90/

class MinStack {
public:
    stack s1, s2;
    /** initialize your data structure here. */
    MinStack() {
        
    }
    
    void push(int x) {
        s1.push(x);
        if(s2.empty() || s2.top() >= x) s2.push(x);
    }
    
    void pop() {
        if(s1.top() == s2.top()) s2.pop();
        s1.pop();
    }
    
    int top() {
        return s1.top();
    }
    
    int getMin() {
        return s2.top();
    }
};

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */