Merge pull request doocs#330 from Stackingrule/dev

feat:add Solution.cpp for 0127. Word Ladder

Author: Stackingrule

solution/0100-0199/0127.Word Ladder/Solution.cpp

@@ -0,0 +1,26 @@
+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;
+        unordered_map<string, int> pathCnt{{{beginWord, 1}}};
+        queue<string> q{{beginWord}};
+        while (!q.empty()) {
+            string word = q.front();
+            q.pop();
+            for (int i = 0; i < word.size(); ++i) {
+                string newWord = word;
+                for (char ch = 'a'; ch <= 'z'; ++ch) {
+                    newWord[i] = ch;
+                    if (wordSet.count(newWord) && newWord == endWord) return pathCnt[word] + 1;
+                    if (wordSet.count(newWord) && !pathCnt.count(newWord)) {
+                        q.push(newWord);
+                        pathCnt[newWord] = pathCnt[word] + 1;
+                    }   
+                }
+            }
+        }
+        return 0;
+    }
+};