add: Word Ladder

Author: hijiangtao

README.md

@@ -40,6 +40,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |91|[Decode Ways](https://leetcode.com/problems/decode-ways/) | [JavaScript](./src/decode-ways/res.js)|Medium|
 |93|[Restore IP Addresses](https://leetcode.com/problems/restore-ip-addresses/) | [JavaScript](./src/restore-ip-addresses/res.js)|Medium|
 |120|[Triangle](https://leetcode.com/problems/triangle/) | [JavaScript](./src/triangle/res.js)|Medium|
+|127|[Word Ladder](https://leetcode.com/problems/word-ladder/) | [JavaScript](./src/word-ladder/res.js)|Medium|
 |130|[Surrounded Regions](https://leetcode.com/problems/surrounded-regions/) | [JavaScript](./src/surrounded-regions/res.js)|Medium|
 |133|[Clone Graph](https://leetcode.com/problems/clone-graph/) | [JavaScript](./src/clone-graph/res.js)|Medium|
 |136|[Single Number](https://leetcode.com/problems/single-number/) | [JavaScript](./src/single-number/res.js)|Easy|

src/word-ladder/res.js

@@ -0,0 +1,59 @@
+/**
+ * res.js
+ * @authors Joe Jiang ([email protected])
+ * @date    2017-06-21 23:22:33
+ * 
+ * 127. Word Ladder
+ * Problem: https://leetcode.com/problems/word-ladder/
+ * Discuss: https://discuss.leetcode.com/category/135/word-ladder
+ *
+ * * Traditional
+ * * Two-end BFS
+ * * Dijkstra's algorithm
+ * 
+ * @param {string} beginWord
+ * @param {string} endWord
+ * @param {string[]} wordList
+ * @return {number}
+ */
+let ladderLength = function(beginWord, endWord, wordList) {
+    wordList.push(endWord);
+    let toVisit = new Set(),
+        wordDict = new Set(wordList),
+        dist = 2;
+    
+    if (wordList.length === wordDict.size) return 0;
+    addNextWords(beginWord, wordDict, toVisit);
+    
+    while (toVisit.size > 0) {
+        let entriesLen = toVisit.size,
+            mark = 0;
+        
+        for (let item of toVisit.values()) {
+            if (mark++ === entriesLen) break;
+            toVisit.delete(item);
+            
+            if (item === endWord) return dist;
+            addNextWords(item, wordDict, toVisit);
+        }
+        
+        dist++;
+    }
+    
+    return 0;
+};
+
+let addNextWords = function(word, wordDict, toVisit) {
+    wordDict.delete(word);
+    let len = word.length;
+    
+    for (let i=0; i<len; i++) {
+        for (let j=97; j<123; j++) {
+            let tmp = word.substring(0, i) + String.fromCharCode(j) + word.substring(i+1, len);
+            if (wordDict.has(tmp)) {
+                toVisit.add(tmp);
+                wordDict.delete(tmp);
+            }
+        }
+    }
+};