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

Implement the MinStack class:

• MinStack() initializes the stack object
• void push(int val) pushes the element val onto the stack
• void pop() removes the element on the top of the stack
• int top() gets the top element of the stack
• int getMin() retrieves the minimum element in the stack

You must implement a solution with O(1) time complexity for each function.

Example

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); // return -3
minStack.pop();
minStack.top();    // return 0
minStack.getMin(); // return -2

Constraints

• -2³¹ <= val <= 2³¹ - 1
• Methods pop, top and getMin operations will always be called on non-empty stacks
• At most 3 * 10⁴ calls will be made to push, pop, top, and getMin

How the tests work: each test is a sequence of calls. operations[i] is the method called with arguments[i]; the first entry constructs the class. The expected output lists what every call returns — null for the constructor and for methods that return nothing.