Min Stack

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

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.

Example:


                    MinStack minStack = new MinStack();
                    

                    minStack.push(-2);
                    

                    minStack.push(0);
                    

                    minStack.push(-3);
                    

                    minStack.getMin();   --> Returns -3.
                    

                    minStack.pop();
                    

                    minStack.top();      --> Returns 0.
                    

                    minStack.getMin();   --> Returns -2.