The sword refers to offer30

#include<iostream>
#include<stack>
using namespace std;

class Solution {
public:
	stack<int>a, b;
	int min() {
		if(!b.empty()) return b.top();
		else return -1;
	}
	int pop() {
		if (!a.empty()) {
			int x = a.top();
			if (x == b.top()) b.pop();
			a.pop();
			return x;
		}
		else return -1;
	}
	void push(int x) {
		if (a.empty() && b.empty())
		{
			a.push(x);
			b.push(x);
		}
		else if(x<b.top()){
			b.push(x);
			a.push(x);
		}
		else {
			a.push(x);
		}
	}

};


int main() {
	Solution s;
	s.push(1);
	cout << s.min() << endl;
	s.push(0);
	cout << s.min() << endl;
	s.push(3);
	cout << s.min() << endl;
	s.pop();
	cout << s.min() << endl;
	s.pop();
	cout << s.min() << endl;
	s.pop();
	cout << s.min() << endl;
	return 0;
}