Min Stack

Medium

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time. Implement MinStack with push(val), pop(), top(), and getMin().

Example 1

Input:  operations = ["MinStack","push","push","push","getMin","pop","top","getMin"], values = [[],[-2],[0],[-3],[],[],[],[]]
Output: [null,null,null,null,-3,null,0,-2]

Constraints

• -2^31 <= val <= 2^31 - 1
• pop, top, getMin are only called on non-empty stacks.
• At most 3*10^4 calls.