Min Stack (Design)

Min Stack (Design)

Design a stack that supports push, pop, top, and retrieving the minimum element, all in O(1). Write createMinStack() returning an object with:

• push(x), push x.
• pop(), remove the top.
• top(), return the top without removing it.
• getMin(), return the current minimum.

The trick: alongside the main stack, keep a second "min stack" whose top is always the current minimum, so getMin never has to scan.

const s = createMinStack();
s.push(-2); s.push(0); s.push(-3);
s.getMin(); // -3
s.pop();
s.top();    // 0
s.getMin(); // -2