word ladder

word_ladder.md

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+1回目。答えを見た。
+変数名がキャメルケースなのは違和感があるが、入力がキャメルケースなので少し納得した。
+
+```py
+from collections import deque
+
+class Solution:
+    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
+        wordSet = set(wordList)
+        if endWord not in wordSet:
+            return 0
+
+        queue = deque([(beginWord, 1)])
+        while queue:
+            word, steps = queue.popleft()
+            if word == endWord:
+                return steps
+
+            for i in range(len(word)):
+                for ch in range(26):
+                    transformed = word[:i] + chr(ord('a') + ch) + word[i+1:]
+                    if transformed in wordSet:
+                        wordSet.remove(transformed)
+                        queue.append((transformed, steps + 1))
+        return 0
+```
+
+2回目。変数をリネームした（入力はそのままキャメルケースだが、新たに宣言する変数はスネークケースにした。混在するのは欠点だが、入力とローカル変数の区別がしやすい利点もある）。
+
+```py
+from collections import deque
+
+class Solution:
+    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
+        word_set = set(wordList)
+        if endWord not in word_set:
+            return 0
+
+        queue = deque([(beginWord, 1)])
+
+        while queue:
+            word, num_steps = queue.popleft()
+
+            if word == endWord:
+                return num_steps
+
+            for i in range(len(word)):
+                for alpha_offset in range(26):
+                    transformed_word = word[:i] + chr(ord('a') + alpha_offset) + word[i + 1:]
+                    if transformed_word in word_set:
+                        word_set.remove(transformed_word)
+                        queue.append((transformed_word, num_steps + 1))
+        return 0
+```
+
+3回目。
+
+```py
+from collections import deque
+
+class Solution:
+    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
+        word_set = set(wordList)
+        if endWord not in word_set:
+            return 0
+
+        queue = deque([(beginWord, 1)])
+
+        while queue:
+            word, num_steps = queue.popleft()
+            if word == endWord:
+                return num_steps
+            for i in range(len(word)):
+                for alpha_offset in range(26):
+                    transformed_word = word[:i] + chr(ord('a') + alpha_offset) + word[i + 1:]
+                    if transformed_word in word_set:
+                        word_set.remove(transformed_word)
+                        queue.append((transformed_word, num_steps + 1))
+        return 0
+```