127. Word Ladder

127-word-ladder/memo.md

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+### step1
+
+BFSでbeginWordから1文字ずつ変えながら探索する方法で実装。
+
+### step2
+
+qの名前をwordToCountに変更。
+
+### step3
+
+3回通すまで書き直し。

127-word-ladder/step1.cpp

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+class Solution {
+public:
+    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
+        unordered_set<string> wordSet(wordList.begin(), wordList.end());
+
+        if (!wordSet.count(endWord)) {
+            return 0;
+        }
+
+        queue<pair<string, int>> q;
+        q.push({ beginWord, 1 });
+
+        while (!q.empty()) {
+            auto [word, steps] = q.front();
+            q.pop();
+            for (int i = 0; i < word.size(); i++) {
+                string temp = word;
+                for (char c = 'a'; c <= 'z'; c++) {
+                    temp[i] = c;
+                    if (temp == endWord) {
+                        return steps + 1;
+                    }
+                    if (wordSet.count(temp)) {
+                        q.push({ temp, steps + 1 });
+                        wordSet.erase(temp);
+                    }
+                }
+            }
+        }
+        return 0;
+    }
+};

127-word-ladder/step2.cpp

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+class Solution {
+public:
+    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
+        unordered_set<string> wordSet(wordList.begin(), wordList.end());
+
+        if (!wordSet.count(endWord)) {
+            return 0;
+        }
+
+        queue<pair<string, int>> wordToCount;
+        wordToCount.push({ beginWord, 1 });
+
+        while (!wordToCount.empty()) {
+            auto [word, steps] = wordToCount.front();
+            wordToCount.pop();
+            for (int i = 0; i < word.size(); i++) {
+                string temp = word;
+                for (char c = 'a'; c <= 'z'; c++) {
+                    temp[i] = c;
+                    if (temp == endWord) {
+                        return steps + 1;
+                    }
+                    if (wordSet.count(temp)) {
+                        wordToCount.push({ temp, steps + 1 });
+                        wordSet.erase(temp);
+                    }
+                }
+            }
+        }
+        return 0;
+    }
+};

127-word-ladder/step3.cpp

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+class Solution {
+public:
+    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
+        unordered_set<string> wordSet(wordList.begin(), wordList.end());
+
+        if (!wordSet.count(endWord)) {
+            return 0;
+        }
+
+        queue<pair<string, int>> wordToCount;
+        wordToCount.push({ beginWord, 1 });
+
+        while (!wordToCount.empty()) {
+            auto [word, steps] = wordToCount.front();
+            wordToCount.pop();
+            for (int i = 0; i < word.size(); i++) {
+                string temp = word;
+                for (char c = 'a'; c <= 'z'; c++) {
+                    temp[i] = c;
+                    if (temp == endWord) {
+                        return steps + 1;
+                    }
+                    if (wordSet.count(temp)) {
+                        wordToCount.push({ temp, steps + 1 });
+                        wordSet.erase(temp);
+                    }
+                }
+            }
+        }
+        return 0;
+    }
+};