Solve Problem 875 - Koko Eating Bananas

Author: Hieu Luong

src/binarysearch/Problem875_KokoEatingBananas.java

@@ -0,0 +1,42 @@
+package binarysearch;
+
+public class Problem875_KokoEatingBananas {
+
+    public int minEatingSpeed(int[] piles, int H) {
+        // min(K) : eat all piles & times <= H
+        // [3,6,7,11]
+        // K = 11 -> 4 hours
+        // K = 8 -> 5 hours
+        // K = 6 -> 1 + 1 + 2 + 2 = 6 hours
+        // K = 5 -> 1 + 2 + 2 + 3 = 8 hours
+        // K = 4 -> 1 + 2 + 2 + 3 = 8 hours
+        // K = 3 -> 1 + 2 + 3 + 4 > 8 hours
+
+        // lo = 1, hi = max;
+        // function(mid) <= H --> hi = mid-1
+        // function(mid) > H --> lo = mid+1
+        // return lo
+
+        int lo = 1, hi = 0;
+        for (int pile: piles) hi = Math.max(hi, pile);
+
+        while (lo <= hi) {
+            int mid = lo + (hi-lo)/2;
+            if (timeToEatAll(piles, mid) <= H) hi = mid-1;
+            else lo = mid+1;
+        }
+        return lo;
+    }
+
+    private int timeToEatAll(int[] piles, int speed) {
+        int res = 0;
+        for (int pile : piles) {
+            if (speed >= pile) res += 1;
+            else {
+                res += pile/speed;
+                if (pile%speed != 0) res++;
+            }
+        }
+        return res;
+    }
+}