Koko Eating Bananas (Binary Search on Answer)

A monkey has n piles of bananas and h hours. Each hour she picks one pile and eats up to k bananas from it (if the pile has fewer than k, she finishes it and waits for the next hour). Find the smallest whole number k that lets her finish every pile within h hours.

Eating a pile of p bananas at speed k takes ⌈p / k⌉ hours.

Input:

• line 1: n h
• line 2: the n pile sizes

Output: the minimum speed k.

Constraints: 1 ≤ n ≤ 10⁴, n ≤ h ≤ 10⁹, 1 ≤ pile ≤ 10⁹.

Think about it: if speed k works, every faster speed works too. That monotone yes/no lets you binary search on the answer between 1 and the biggest pile.