Min Stack - Medium Python Stack Interview Problem

Design a stack that supports push, pop, top, and getMin - all in O(1) time.

Implement the MinStack class:

MinStack() - initializes the stack.
push(val) - pushes val onto the stack.
pop() - removes the top element.
top() - returns the top element without removing it.
getMin() - returns the minimum element currently in the stack.

Example

Input: ["MinStack","push","push","push","getMin","pop","top","getMin"]
       [[],[-2],[0],[-3],[],[],[],[]]
Output: [null,null,null,null,-3,null,0,-2]
Explanation: After pushing -2, 0, -3, the minimum is -3. After popping -3, top is 0 and minimum is -2.

Constraints

-2^31 <= val <= 2^31 - 1
pop, top, and getMin are always called on a non-empty stack.
At most 3 * 10^4 calls will be made.

Hints