22. Min StackMedium

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

Implement a stack with push, pop, top, and getMin. getMin should return the smallest value currently in the stack.

The minimum must reflect the current stack after previous pushes and pops. A value that was popped should no longer influence getMin.

Examples

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

Input: operations = ["MinStack","push","push","top","getMin","pop","getMin"], values = [null,2,1,null,null,null,null]
Output: [null,null,null,1,1,null,2]

Constraints

1 <= operations.length <= 20,000
operations[i] is one of MinStack, push, pop, top, or getMin.
values[i] is null unless operations[i] is push.