LeetCode_155. Min Stack

题目描述：

思路：设置两个$stack$，$data$和$min\_data$，分别用于存放加入stack中的数据和stack中最小的数据。

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {
        
    }
    
    void push(int x) {
        data.push(x);
        //min_data为空，则当前元素就是栈中最小的元素
        if(min_data.empty())
            min_data.push(x);
        //和栈顶元素比较大小，决定加入的元素是什么
        else{
            if(x<min_data.top())
                min_data.push(x);
            else
                min_data.push(min_data.top());
        }
    }
    
    void pop() {
        data.pop();
        min_data.pop();
    }
    
    int top() {
        if(!data.empty())
            return data.top();
        else
            return -1;
    }
    
    int getMin() {
        if(!min_data.empty())
            return min_data.top();
        else
            return -1;
    }
private:
    stack<int> data;
    stack<int> min_data;
};

/**
 * 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();
 */