Create 1011. Capacity To Ship Packages Within D Days.md

1011. Capacity To Ship Packages Within D Days/1011. Capacity To Ship Packages Within D Days.md

@@ -0,0 +1,132 @@
+# 1011. Capacity To Ship Packages Within D Days
+## STEP1
+- 何も見ずに解いてみる
+- 船のキャパシティを range として用意し、days 以内で運び出せるかどうかを判定する。True となる最小のキャパシティを探索する。
+
+```python
+import bisect
+
+
+MAX_WEIGHT = 500
+MAX_WEIGHT_LENGTH = 50_000
+
+
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        def can_ship_within_days(ship_capacity: int) -> bool:
+            num_days = 1
+            total_weight_at_a_day = 0
+            for weight in weights:
+                if weight > ship_capacity:
+                    return False
+                total_weight_at_a_day += weight
+                if total_weight_at_a_day <= ship_capacity:
+                    continue
+                num_days += 1
+                total_weight_at_a_day = weight
+            return num_days <= days
+
+        return bisect.bisect_left(
+            range(MAX_WEIGHT * MAX_WEIGHT_LENGTH + 1),
+            True,
+            key=can_ship_within_days
+        )
+```
+
+## STEP2
+### プルリクやドキュメントを参照
+- range を bisect_left の引数として良いかは自信がなかった。
+    - https://docs.python.org/3/library/stdtypes.html#typesseq-range
+    - range は空間計算量 O(1) で、 common sequence operations としてランダムアクセスも実装されていそうなので、動く。
+
+- https://github.com/olsen-blue/Arai60/pull/44/files
+    - 探索区間について、[max(weights), sum(weights)] でよい。船のキャパの下限を、全ての荷物一つが乗るサイズとすると、空の船に荷物が乗らない状況を考えなくて済む。
+    - days が 0 の場合、STEP1のコードは MAX_WEIGHT * MAX_WEIGHT_LENGTH + 1 を返す。意味はないので 0 は ValueError とした方がよい。
+
+```python
+import bisect
+
+
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        if days <= 0:
+            raise ValueError("days must be positive.")
+
+        def can_ship_within_days(ship_capacity: int) -> bool:
+            days_required = 1
+            total_weight = 0
+            for weight in weights:
+                total_weight += weight
+                if total_weight <= ship_capacity:
+                    continue
+                days_required += 1
+                total_weight = weight
+            return days_required <= days
+
+        return bisect.bisect_left(
+            range(sum(weights) + 1),
+            True,
+            lo=max(weights),
+            key=can_ship_within_days
+        )
+```
+
+練習として2分探索を書く。
+```python
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        if days <= 0:
+            raise ValueError("days must be positive.")
+
+        def can_ship_within_days(ship_capacity: int) -> bool:
+            days_required = 1
+            total_weight = 0
+            for weight in weights:
+                total_weight += weight
+                if total_weight <= ship_capacity:
+                    continue
+                days_required += 1
+                total_weight = weight
+            return days_required <= days
+
+        low = max(weights)
+        high = sum(weights)
+        while low < high:
+            middle = (low + high) // 2
+            if can_ship_within_days(middle):
+                high = middle
+            else:
+                low = middle + 1
+        return low
+```
+## STEP3
+### 3回ミスなく書く
+```python
+import bisect
+
+
+class Solution:
+    def shipWithinDays(self, weights: List[int], days: int) -> int:
+        if days <= 0:
+            raise ValueError("days must be positive")
+
+        def can_ship_within_days(ship_capacity: int) -> bool:
+            total_weight = 0
+            days_required = 1
+            for weight in weights:
+                total_weight += weight
+                if total_weight <= ship_capacity:
+                    continue
+                days_required += 1
+                total_weight = weight
+            return days_required <= days
+
+        return bisect.bisect_left(
+            range(sum(weights) + 1),
+            True,
+            lo=max(weights),
+            key=can_ship_within_days
+        )
+```
+
+3分,3分,3分で3回Accept