307. Koko Eating Bananas

Koko loves to eat bananas. There are n piles of bananas, where the i-th pile has piles[i] bananas. The guards will return in h hours. Koko can decide her bananas-per-hour eating speed k. Each hour, she chooses a pile and eats k bananas from it. If the pile has fewer than k bananas, she eats all of them and waits for the next hour. Return the minimum integer k such that she can eat all the bananas within h hours.