Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

class MinStack {
public:
    void push(int x) {
        if(sta.size() == 0){
            sta.push(x);
            min.push(x);
        }
        else{
            if(x <= min.top()) min.push(x);
            sta.push(x);
        }
    }

    void pop() {
        if(min.top() == sta.top()){
            sta.pop();
            min.pop();
        }
        else sta.pop();
    }

    int top() {
        return sta.top();
    }

    int getMin() {
        return min.top();
    }
private:
    stack<int> sta;
    stack<int> min;
};