Merge pull request #1809 from wang2jun/master

添加 127单词接龙 TypeScript 版本代码

problems/0127.单词接龙.md

@@ -247,6 +247,55 @@ var ladderLength = function(beginWord, endWord, wordList) {
 };
 ```
 
+## TypeScript
+```typescript
+function ladderLength(
+  beginWord: string,
+  endWord: string,
+  wordList: string[]
+): number {
+  const words = new Set(wordList);
+  if (!words.has(endWord)) return 0;
+  if (beginWord.length === 1) return 2;
+  let current = new Set([beginWord]);
+  let rightcurrent = new Set([endWord]);
+  words.delete(endWord);
+  let step = 1;
+  while (current.size) {
+    if (current.size > rightcurrent.size) {
+      [current, rightcurrent] = [rightcurrent, current];
+    }
+    const temp: Set<string> = new Set();
+    for (const word of current) {
+      for (const right of rightcurrent) {
+        if (diffonechar(word, right)) {
+          return step + 1;
+        }
+      }
+      for (const other of words) {
+        if (diffonechar(other, word)) {
+          temp.add(other);
+
+          words.delete(other);
+        }
+      }
+    }
+    if (temp.size === 0) return 0;
+    current = temp;
+    step = step + 1;
+  }
+  return 0;
+}
+
+function diffonechar(word1: string, word2: string): boolean {
+  let changes = 0;
+  for (let i = 0; i < word1.length; i++) {
+    if (word1[i] != word2[i]) changes += 1;
+  }
+  return changes === 1;
+}
+```
+
 
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