Leetcode127 - Word Ladder

//展示代码 - BFS 和 code style
class Solution {
    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
    Set<String> wordSet = new HashSet<>();
    for(String aWord: wordList) {
        wordSet.add(aWord);
    }   
    Queue<String> queue = new LinkedList<>();
    queue.offer(beginWord);
    int distance = 1;
    while (!queue.isEmpty() && !wordSet.isEmpty()) {
        Queue<String> queue2 = new LinkedList<>();
        distance++;
        while (!queue.isEmpty()) {
            String top = queue.poll();
            ArrayList<String> wordsWithinDistance =
                getWordsWithinDistance(wordSet, top);
            if (wordsWithinDistance.contains(endWord)) {
                return distance;
            }
            queue2.addAll(wordsWithinDistance);
        }
        queue = queue2;
    }
    return 0;
    }
    
    public ArrayList<String> getWordsWithinDistance(Set<String> wordSet, String word) {
    ArrayList<String> results = new ArrayList<>();
    char[] wordCharArr = word.toCharArray();
    for (int i = 0; i < word.length(); i++) {
        char oriChar = wordCharArr[i];
        for (char c = 'a'; c <= 'z'; c++) {
            if (c == oriChar) {
                continue;
            }
            wordCharArr[i] = c;
            String newStr = new String(wordCharArr);
            if (wordSet.contains(newStr)) {
                results.add(newStr);
                wordSet.remove(newStr);
            }
        }
        wordCharArr[i] = oriChar;
    }
    return results;
    }  
}