301. Min Stack

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.
• push(val) pushes the element val onto the stack.
• pop() removes the element on the top of the stack.
• top() gets the top element of the stack.
• getMin() retrieves the minimum element in the stack.

Examples

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