[LintCode] 带最小值操作的栈

class MinStack {
public:
MinStack() {
// do initialization if necessary
}

void push(int number) {
// write your code here
if (minimum.empty() || number <= minimum.top())
minimum.push(number);
data.push(number);
}

int pop() {
// write your code here
if (minimum.top() == data.top())
minimum.pop();
int elem = data.top();
data.pop();
return elem;
}

int min() {
// write your code here
return minimum.top();
}
private:
stack<int> data;
stack<int> minimum;
};