Solution: Koko Eating Bananas

Statement

Koko has $n$ piles of bananas in front of her, where the $i^{th}$ pile has piles[i] bananas. The guards have left and will return in h hours, and Koko must finish all the bananas before they come back.

Before eating, Koko chooses an integer as an eating speed $k$ (bananas per hour). She keeps this speed constant throughout.

In each hour, Koko selects one pile of bananas and eats from it according to the following rules:

• If the pile contains at least $k$ bananas, she eats exactly $k$ bananas from it.

• If the pile contains fewer than $k$ bananas, she eats all the bananas from that pile and does not eat from any other pile during that hour.

Your task is to return the minimum eating speed $k$ ...