JS Practice — Built-in Objects

Stack-based Min Tracker

📖 Usage Example

class MinStack {
  constructor() { this.stack = []; this.mins = []; }
  push(v) {
    this.stack.push(v);
    this.mins.push(Math.min(v, this.mins.at(-1) ?? v));
  }
  min() { return this.mins.at(-1); }
}

Track minimums in O(1) by maintaining a parallel stack of running minimums.

Stack with Min Tracking

Design a Stack that supports pushing, popping, and tracking the minimum element efficiently in O(1) time.

Challenge: Without auxiliary space, finding min is O(n). With a helper stack, it's O(1).

Operations:

push(x): Add element
pop(): Remove element
getMin(): Return current minimum in O(1)

class MinStack {
  push(x: number): void {}
  pop(): number | undefined {}
  getMin(): number | undefined {}
}

const ms = new MinStack()
ms.push(3)
ms.push(1)
ms.push(2)
ms.getMin() // 1

💡 Hints (5)

• Use two stacks: one for elements, one for minimums.
• When pushing, check if it's less than or equal to the current min.
• When popping, check if it was the current min and pop from minStack too.
• getMin returns the top of the minStack.
• This keeps getMin at O(1) instead of O(n).