【数据结构与算法面试题】包含min函数的栈

template <class Type> class min_stack{
	private:
		stack<Type> s1;
		stack<Type> s2;
	public:
		min_stack(){}
		~min_stack(){}

		Type min(){
			if (!s2.empty()){
				return s2.top();
			}
		}

		void push(Type a){
			s1.push(a);
			if (s2.empty() || a <= s2.top()){
				s2.push(a);
			}
		}

		Type pop(){
			if (!s1.empty() && !s2.empty()){// 非空
				if (s1.top() == s2.top()){
					s2.pop();
				}
				return s1.pop();
			}
		}
};