1011. Capacity To Ship Packages Within D Days

medium/1011/answer.md

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+# Step1
+
+かかった時間：33min
+
+計算量：N = len(weights), M = sum(weights)として
+
+時間計算量：O(NlogM)
+
+空間計算量：O(1)
+
+```python
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        def can_ship_capacity_in_days(capacity: int, days: int) -> bool:
+            total_weight = 0
+            i = 0
+            while days:
+                if total_weight + weights[i] > capacity:
+                    total_weight = 0
+                    days -= 1
+                    continue
+
+                total_weight += weights[i]
+                i += 1
+                if i == len(weights):
+                    return True
+
+            return False
+
+        left = 1
+        right = sum(weights)
+        while left < right:
+            middle = (left + right) // 2
+            if can_ship_capacity_in_days(middle, days):
+                right = middle
+            else:
+                left = middle + 1
+
+        return left
+```
+思考ログ：
+- 問題を読み違えて時間を無駄にしていた（weightsの順序を保つ制約を無視していた）
+- 二分探索の探索用変数の名前を横着している、step2以降なんとかする
+- 類似の問題を昔解いたのを覚えていた
+  - あるcapacityにした時、days内で輸送できるか考える
+  - capacity = sum(weights)とすれば、必ず1日で輸送できる
+  - 輸送できるcapacityのうち最小のものを探す
+    - [輸送できない, 輸送できない, ..., 輸送できない, (輸送できる], 輸送できる, ... ,輸送できる]
+
+# Step2
+
+講師役目線でのセルフツッコミポイント：
+- weights=[], days=0の時は？
+
+参考にした過去ログなど：
+- https://github.com/saagchicken/coding_practice/pull/15
+  - 探索範囲は1からでなくmax(weights)からでいい
+- https://github.com/saagchicken/coding_practice/pull/10
+- https://github.com/olsen-blue/Arai60/pull/44
+- https://github.com/hroc135/leetcode/pull/42
+  - goのbinary-searchの実装  
+- https://github.com/Ryotaro25/leetcode_first60/pull/51
+  - Makefileについて
+- https://github.com/Mike0121/LeetCode/pull/46
+- https://github.com/Yoshiki-Iwasa/Arai60/pull/37
+- https://github.com/rossy0213/leetcode/pull/26
+- https://github.com/goto-untrapped/Arai60/pull/41
+- https://github.com/fhiyo/leetcode/pull/45
+  - https://github.com/fhiyo/leetcode/pull/45/files#r1682470839
+- https://github.com/sakupan102/arai60-practice/pull/45
+- https://github.com/SuperHotDogCat/coding-interview/pull/27
+  - https://github.com/SuperHotDogCat/coding-interview/pull/27/files#r1631399685
+  - 命名はなかなか難しいなと
+  - 実態を表すよう無理に情報を詰め込むと拗らせるので、そういう場合はなるべくシンプルにして、必要ならコメント補足を心掛ける
+- https://github.com/YukiMichishita/LeetCode/pull/10
+  - bisect_left/right
+    - bisect_rightを勘違いしていた（等号は含まない）
+      - https://docs.python.org/ja/3.13/library/bisect.html  
+        >  all(elem > x for elem in a[ip : hi]) is true for the right slice.
+- https://github.com/shining-ai/leetcode/pull/44
+- https://github.com/hayashi-ay/leetcode/pull/55
+
+所要日数を計算する
+```python
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        assert days > 0
+        if not weights:
+            return 0
+
+        def calculate_shipping_days(capacity: int) -> int:
+            total_weight = 0
+            days_required = 1
+            for weight in weights:
+                if total_weight + weight > capacity:
+                    total_weight = 0
+                    days_required += 1
+
+                total_weight += weight
+
+            return days_required
+
+        low = max(weights)
+        high = sum(weights)
+        while low < high:
+            candidate_capacity = (low + high) // 2
+            if calculate_shipping_days(candidate_capacity) <= days:
+                high = candidate_capacity
+            else:
+                low = candidate_capacity + 1
+
+        return low
+```
+思考ログ：
+
+bisect_right（練習）
+```python
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        assert days > 0
+        if not weights:
+            return 0
+
+        def can_ship(capacity: int) -> bool:
+            total_weight = 0
+            days_required = 1
+            for weight in weights:
+                if total_weight + weight > capacity:
+                    total_weight = 0
+                    days_required += 1
+
+                total_weight += weight
+
+            return days_required <= days
+
+        return bisect.bisect_right(
+            range(sum(weights) + 1),
+            False,
+            lo=max(weights),
+            hi=sum(weights) + 1,
+            key=can_ship
+        )
+```
+思考ログ：
+- 今回の課題で敢えて使うこともないが、bisect_rightの練習で書いてみた
+- 関数名、```can_ship```くらいでいい気もするので少し変更
+
+# Step3
+
+かかった時間：5min
+
+```python
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        assert days > 0
+        if not weights:
+            return 0
+
+        def can_ship(capacity: int) -> bool:
+            total_weight = 0
+            days_required = 1
+            for weight in weights:
+                if weight > capacity:
+                    return False
+
+                if total_weight + weight > capacity:
+                    total_weight = 0
+                    days_required += 1
+
+                total_weight += weight
+
+            return days_required <= days
+
+        return bisect.bisect_left(
+            range(sum(weights)),
+            True,
+            key=can_ship,
+            lo=max(weights),
+            hi=sum(weights)
+        )
+```
+思考ログ：
+- ```weight > capacity```の早期リターンを追加
+
+# Step4
+
+```python
+```
+思考ログ：