Solution: K Empty Slots

Statement

You are given $n$ bulbs arranged in a row, numbered from $1$ to $n$. Initially, all bulbs are turned off.

Each day, exactly one bulb is switched on. You are given an array, bulbs of length $n$ where bulbs[i] $= x$ means that on day $i + 1$ (1‑indexed), the bulb at position $x$ (also 1‑indexed) is turned on.

So, given an integer k, determine the earliest day (the smallest day number) on which there are two bulbs that are on such that exactly k bulbs are off between them.

If no such day exists, return $-1$ ...