Stack with Min/Max operation constant time.

MinStack.cs

public class MinStack {
    
    private Stack<int> _stack = new Stack<int>();
    private Stack<int> _min = new Stack<int>();
    
    public void Push(int x) {
        _stack.Push(x);    
        
        if(_min.Count == 0) _min.Push(x);
        else {
            if(x <= _min.Peek()) 
                _min.Push(x);
        }
    }

    public void Pop() {
        
        if(_stack.Pop() == _min.Peek())
            _min.Pop();
    }

    public int Top() {
        return _stack.Peek();
    }

    public int GetMin() {
        return _min.Peek();
    }
}