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.

You must implement a solution with O(1) time complexity for each function.

Examples

Example 1:

Input:

`

["MinStack","push","push","push","getMin","pop","top","getMin"]

[[],[-2],[0],[-3],[],[],[],[]]

`

Output: [null,null,null,null,-3,null,0,-2]

Explanation:

`

MinStack minStack = new MinStack();

minStack.push(-2);

minStack.push(0);

minStack.push(-3);

minStack.getMin(); // return -3

minStack.pop();

minStack.top(); // return 0

minStack.getMin(); // return -2

`

Constraints

• -2^31 <= val <= 2^31 - 1
• Methods pop, top and getMin operations will always be called on non-empty stacks
• At most 3 * 10^4 calls will be made to push, pop, top, and getMin