Koko Eating Bananas

0875.Koko-Eating-Bananas/memo.md

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+# 875. Koko Eating Bananas
+
+## step1
+二分探索を思いつく。時間計算量はO(nlog max(piles))。17mほど。最小値と最大値を何度か間違えた（ガチャを引いてしまった）。
+
+とりあえず書いた答えを残す。
+
+改善する。
+
+上限と下限を単純に 1, max(piles)とした方が可読性が上がるが、速度は落ちる。
+
+## step2
+二分探索を手で書く
+
+https://leetcode.com/problems/koko-eating-bananas/solutions/7047251/simple-solution-by-harshita_114-3c0a/
+
+can_eat_all の判定はfor文を使えば早期終了できる場合があるのか
+
+実際の実行時間はジェネレータ表記の方が早かった
+
+https://github.com/yamashita-ki/codingTest/pull/15
+
+https://github.com/Exzrgs/LeetCode/pull/45/changes
+
+https://github.com/TaisukeFujise/leetcode_tafujise/pull/16
+
+## step3
+今回は省略で良いだろう

0875.Koko-Eating-Bananas/step1.py

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+import bisect
+
+
+class Solution:
+    def minEatingSpeed(self, piles: List[int], h: int) -> int:
+        def can_eat_all(k):
+            return sum(((pile + k - 1) // k for pile in piles)) <= h
+
+        candidate = range(
+            max(min(piles) // h, 1),
+            max((max(piles) * 2 - 1) // (h // len(piles)), 1) + 1,
+        )
+        index = bisect.bisect_left(
+            range(len(candidate)), True, key=lambda index: can_eat_all(candidate[index])
+        )
+        return candidate[index]

0875.Koko-Eating-Bananas/step1_revised.py

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+import bisect
+
+
+class Solution:
+    def minEatingSpeed(self, piles: list[int], h: int) -> int:
+        if not piles:
+            return 0
+
+        def can_eat_all(k):
+            return sum(((pile + k - 1) // k for pile in piles)) <= h
+
+        max_candidate = max((max(piles) * 2 - 1) // (h // len(piles)), 1)
+        min_candidate = max(min(piles) // h, 1)
+        candidate = range(min_candidate, max_candidate + 1)
+        index = bisect.bisect_left(
+            range(len(candidate)), True, key=lambda index: can_eat_all(candidate[index])
+        )
+        return candidate[index]

0875.Koko-Eating-Bananas/step2.py

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+class Solution:
+    def minEatingSpeed(self, piles: list[int], h: int) -> int:
+        if not piles:
+            return 0
+
+        def can_eat_all(k):
+            return sum(((pile + k - 1) // k for pile in piles)) <= h
+
+        left = max(min(piles) // h, 1)
+        right = max((max(piles) * 2 - 1) // (h // len(piles)), 1) + 1
+        while left < right:
+            mid = left + (right - left) // 2
+            if not can_eat_all(mid):
+                left = mid + 1
+            else:
+                right = mid
+
+        return left

0875.Koko-Eating-Bananas/step2_early_return.py

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+class Solution:
+    def minEatingSpeed(self, piles: list[int], h: int) -> int:
+        if not piles:
+            return 0
+
+        def can_eat_all(k):
+            hours = 0
+            for i, pile in enumerate(piles):
+                hours += (pile + k - 1) // k
+                if hours + (len(piles) - i - 1) > h:
+                    return False
+            return True
+
+        left = max(min(piles) // h, 1)
+        right = max((max(piles) * 2 - 1) // (h // len(piles)), 1) + 1
+        while left < right:
+            mid = left + (right - left) // 2
+            if not can_eat_all(mid):
+                left = mid + 1
+            else:
+                right = mid
+
+        return left

0875.Koko-Eating-Bananas/step2_revised.py

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+class Solution:
+    def minEatingSpeed(self, piles: list[int], h: int) -> int:
+        if not piles:
+            return 0
+
+        def can_eat_all(k):
+            return sum(((pile + k - 1) // k for pile in piles)) <= h
+
+        left = max(min(piles) // h, 1)
+        right = max((max(piles) * 2 - 1) // (h // len(piles)), 1) + 1
+        while left < right:
+            mid = (left + right) // 2
+            if not can_eat_all(mid):
+                left = mid + 1
+            else:
+                right = mid
+
+        return left