BananaEater.java

public class BananaEater {

    public int minEatingSpeed(int[] piles, int H) {
        int lo = 1, hi = getMaxPile(piles);

        // Binary search to find the smallest valid K.
        while (lo <= hi) {
            int K = lo + ((hi - lo) >> 1);
            if (canEatAll(piles, K, H)) {
                hi = K - 1;
            } else {
                lo = K + 1;
            }
        }

        return lo;
    }

    private boolean canEatAll(int[] piles, int K, int H) {
        int countHour = 0; // Hours take to eat all bananas at speed K.

        for (int pile : piles) {
            countHour += pile / K;
            if (pile % K != 0)
                countHour++;
        }
        return countHour <= H;
    }

    private int getMaxPile(int[] piles) {
        int maxPile = Integer.MIN_VALUE;
        for (int pile : piles) {
            maxPile = Math.max(pile, maxPile);
        }
        return maxPile;
    }

    public static void main(String[] args) {
        BananaEater eater = new BananaEater();

        int[] piles1 = {3, 6, 7, 11};
        int h1 = 8;
        assert eater.minEatingSpeed(piles1, h1) == 4 : "Test case 1 failed";

        int[] piles2 = {30, 11, 23, 4, 20};
        int h2 = 5;
        assert eater.minEatingSpeed(piles2, h2) == 30 : "Test case 2 failed";

        int[] piles3 = {30, 11, 23, 4, 20};
        int h3 = 6;
        assert eater.minEatingSpeed(piles3, h3) == 23 : "Test case 3 failed";

        System.out.println("All test cases passed!");
    }
}