Min Stack
Difficulty: Medium
Category: DSA
Topics: Stack, Design
Asked at: Capital One, Amazon, Bloomberg, Microsoft, Oracle, eBay, Apple, Coupang
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.
**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:**
- `-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`.