剑指offer--27.包含min函数的栈

class Solution {
public:
    void push(int value) {
        data.push(value);
        if(minnum.empty())
            minnum.push(value);
        else if(minnum.top()<value)
            minnum.push(minnum.top());
        else
            minnum.push(value);
    }
    void pop() {
        if(!data.empty())
        {
            data.pop();
            minnum.pop();
        }
    }
    int top() {
        return data.top();
    }
    int min() {
        return minnum.top();
    }
private:
    stack<int> data;
    stack<int> minnum;
};