994. Rotting Oranges

994. Rotting Oranges.md

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+### Step1
+
+- 内包表記を多用してみた。どうだろうか。
+    - 意図は明確になるように感じるけど、長くなりがち？
+- minites_plus_oneは流石にわかりにくいかも。
+    - while oranges_rottenのすぐ後でminites_plus_one += 1したいなあと思ってたらこうなってしまった。
+- あとで気づいたが、xとyが逆でした
+
+```python
+class Solution:
+    EMPTY = 0
+    FRESH = 1
+    ROTTEN = 2
+
+    def orangesRotting(self, grid: List[List[int]]) -> int:
+        rotting_grid = [row[:] for row in grid]
+
+        def rot_orange_if_fresh(x: int, y: int) -> None:
+            if not 0 <= x < len(grid) or not 0 <= y < len(grid[0]):
+                return
+            if rotting_grid[x][y] != self.FRESH:
+                return
+            rotting_grid[x][y] = self.ROTTEN
+            rotting_oranges.append((x, y))
+
+        minites_plus_one = 0
+        if all(cell == self.EMPTY for row in grid for cell in row):
+            return 0
+        oranges_rotten = [(x, y) for y in range(len(grid[0])) for x in range(len(grid)) if grid[x][y] == self.ROTTEN]
+        while oranges_rotten:
+            minites_plus_one += 1
+            rotting_oranges = []
+            for x, y in oranges_rotten:
+                rot_orange_if_fresh(x + 1, y)
+                rot_orange_if_fresh(x - 1, y)
+                rot_orange_if_fresh(x, y + 1)
+                rot_orange_if_fresh(x, y - 1)
+            oranges_rotten = rotting_oranges
+        if any(cell == self.FRESH for row in rotting_grid for cell in row):
+            return -1
+        return minites_plus_one - 1
+```
+
+## Step2
+
+- deepcopyする必要なかった、、、
+- 以下の悩んだポイント
+    - いくらなんでも繰り返し多すぎ？ただ、関数化するとしてもどこまで関数化するかが難しい。
+    - x, yはdataclassとかにした方がいいだろうか、大袈裟？
+
+```python
+class Solution: 
+    EMPTY = 0
+    FRESH = 1
+    ROTTEN = 2
+
+    def get_initial_rotten_oranges_num_and_coordinates(self, grid: List[List[int]]) -> Tuple[int, Set[Tuple[int, int]]]:
+        num_rotten = 0
+        coordinates_rotten = set()
+        for y in range(len(grid)):
+            for x in range(len(grid[0])):
+                if grid[y][x] != self.ROTTEN:
+                    continue
+                num_rotten += 1
+                coordinates_rotten.add((x, y))
+        return num_rotten, coordinates_rotten
+
+    def count_oranges(self, grid: List[List[int]]) -> int:
+        num_oranges = 0
+        for y in range(len(grid)):
+            for x in range(len(grid[0])):
+                if grid[y][x] == self.EMPTY:
+                    continue
+                num_oranges += 1
+        return num_oranges
+
+    def is_fresh(self, x: int, y: int, grid: List[List[int]], coordinates_rotten: Set[Tuple[int, int]]) -> bool:
+        if not 0 <= x < len(grid[0]) or not 0 <= y < len(grid):
+            return False
+        if grid[y][x] == self.EMPTY:
+            return False
+        if (x, y) in coordinates_rotten:
+            return False
+        return True
+
+    def orangesRotting(self, grid: List[List[int]]) -> int:
+        num_rotten, coordinates_rotten = self.get_initial_rotten_oranges_num_and_coordinates(grid)
+        num_all_oranges = self.count_oranges(grid)
+        previously_rotten = list(coordinates_rotten)
+        result = 0
+        while True:
+            rotting = []
+            if num_rotten == num_all_oranges:
+                return result
+            if not previously_rotten:
+                return -1
+            for x, y in previously_rotten:
+                if self.is_fresh(x + 1, y, grid, coordinates_rotten):
+                    num_rotten += 1
+                    coordinates_rotten.add((x + 1, y))
+                    rotting.append((x + 1, y))
+                if self.is_fresh(x - 1, y, grid, coordinates_rotten):
+                    num_rotten += 1
+                    coordinates_rotten.add((x - 1, y))
+                    rotting.append((x - 1, y))
+                if self.is_fresh(x , y + 1, grid, coordinates_rotten):
+                    num_rotten += 1
+                    coordinates_rotten.add((x , y + 1))
+                    rotting.append((x , y + 1))
+                if self.is_fresh(x, y - 1, grid, coordinates_rotten):
+                    num_rotten += 1
+                    coordinates_rotten.add((x , y - 1))
+                    rotting.append((x , y - 1))
+            previously_rotten = rotting
+            result += 1
+
+```
+
+https://discord.com/channels/1084280443945353267/1200089668901937312/1201562858295656599
+
+- 上の自分のコードは、関係性がある(lenとか差集合とかの関連がある)変数が多い割にそれぞれ別で処理しているので、追うのが大変になってるかも。変数管理が大変？
+- set()のメソッドを読む
+    - https://docs.python.org/3/library/stdtypes.html#set
+    - remove(elem)とかdiscard(elem)とか知らなかった(昔見たかもしれないが、忘れていた)
+        - 前者はelemがない場合ValueError, 後者は単に無視
+- IntEnumが便利そう
+    - 0, 1, 2以外が入っても、型チェックをonにしたら弾いてくれる
+- num_rottenは、get_initial_oranges_of_rottenで計算せずに、単にlen(rotten_coordinates)でよかったかも
+
+```python
+from enum import IntEnum
+
+class Orange(IntEnum):
+    EMPTY = 0
+    FRESH = 1
+    ROTTEN = 2
+
+class Solution: 
+    def is_fresh(self, grid: List[List[Orange]], x: int, y: int, rotten_so_far: Set[Tuple[int, int]]) -> bool:
+        if not 0 <= x < len(grid[0]) or not 0 <= y < len(grid):
+            return False
+        if grid[y][x] == Orange.EMPTY:
+            return False
+        if (x, y) in rotten_so_far:
+            return False
+        return True
+
+    def count_oranges(self, grid: List[List[Orange]]) -> int:
+        num_oranges = 0
+        for y in range(len(grid)):
+            for x in range(len(grid[0])):
+                if grid[y][x] == Orange.EMPTY:
+                    continue
+                num_oranges += 1
+        return num_oranges
+
+    def get_initial_oranges_of_rotten(self, grid: List[List[Orange]]) -> Tuple[int, Set[Tuple[int, int]]]:
+        rotten_coordinates = set()
+        num_rotten = 0
+        for y in range(len(grid)):
+            for x in range(len(grid[0])):
+                if grid[y][x] != Orange.ROTTEN:
+                    continue
+                rotten_coordinates.add((x, y))
+                num_rotten += 1
+        return num_rotten, rotten_coordinates
+
+    def orangesRotting(self, grid: List[List[Orange]]) -> int:
+        num_rotten, rotten_coordinates = self.get_initial_oranges_of_rotten(grid)
+        previous_rotten = rotten_coordinates.copy()
+        num_oranges = self.count_oranges(grid)
+        minutes = 0
+        while num_rotten < num_oranges:
+            rotting = set()
+            for x, y in previous_rotten:
+                if self.is_fresh(grid, x + 1, y, rotten_coordinates):
+                    rotting.add((x + 1, y))
+                if self.is_fresh(grid, x - 1, y, rotten_coordinates):
+                    rotting.add((x - 1, y))
+                if self.is_fresh(grid, x, y + 1, rotten_coordinates):
+                    rotting.add((x, y + 1))
+                if self.is_fresh(grid, x, y - 1, rotten_coordinates):
+                    rotting.add((x, y - 1))
+            if not rotting:
+                return -1 # impossible
+            rotten_coordinates |= rotting
+            num_rotten += len(rotting)
+            previous_rotten = rotting
+            minutes += 1
+        return minutes
+```