LintCode-劍指Offer-(12)帶最小值操作的棧

class MinStack {
public:
    MinStack() {
        // do initialization if necessary
    }
    stack<int> s;
    stack<int> minstack;
    int minnum;
    void push(int number) {
        // write your code here
        if(s.size()==0)
            minnum=number;
        else if(minnum>number)
            minnum=number;
        minstack.push(minnum);
        s.push(number);
    }

    int pop() {
        int tmp=s.top();
        s.pop();
        minstack.pop();
        if(minstack.size()!=0)
            minnum=minstack.top();
        return tmp;
    }

    int min() {
        return minnum;
        // write your code here
    }
};