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.
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