Koko Eating Bananas

Problem

Koko has piles of bananas and h hours before the guards return. Each hour she chooses a pile and eats up to k bananas from it (if the pile has fewer than k, she finishes it and stops for the hour). Find the minimum integer eating speed k so she can finish all the piles within h hours.

Examples

Example 1

Input:piles = [3,6,7,11], h = 8

Output:4

Example 2

Input:piles = [30,11,23,4,20], h = 5

Output:30

Constraints

1 <= piles.length <= h <= 10^4

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How to approach it: the Binary Search pattern

Repeatedly halve the search space by comparing the middle element to a target, turning an O(n) scan into O(log n). It works on more than sorted arrays — any "answer space" that's monotonic (true…true…false…false) can be binary searched.

Look for this pattern when

The input is sorted, or partially sorted (like a rotated sorted array).
You're minimizing or maximizing a value where "is X feasible?" is easy to check and feasibility is monotonic.

Read the full Binary Search guide →

Video walkthroughs

Original problem on LeetCode ↗