1
class Solution {
2
  public int ladderLength(String beginWord, String endWord, List<String> wordList) {
3
    int count = 1;
4
    Set<String> words = new HashSet<>(wordList);
5
    Queue<String> q = new LinkedList<String>();
6
    q.add(beginWord);
7

8
    while (!q.isEmpty()) {
9
      int size = q.size();
10

11
      while (size-- > 0) {
12
        String word = q.poll();
13
        char[] chList = word.toCharArray();
14

15
        for (int i = 0; i < word.length(); i++) {
16
          char tmp = chList[i];
17

18
          for (char c = 'a'; c <= 'z'; c++) {
19
            chList[i] = c;
20
            String newWord = new String(chList);
21

22
            if (words.contains(newWord)) {
23
              if (newWord.equals(endWord)) {
24
                return count + 1;
25
              }
26
              q.add(newWord);
27
              words.remove(newWord);
28
            }
29
          }
30

31
          chList[i] = tmp;
32
        }
33
      }
34

35
      count++;
36
    }
37

38
    return 0;
39
  }
40
}