LeetCode 127: Word Ladder

Because of lots dups in dict, better to use hash set to filter it out.

class Solution {
    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
        if (beginWord.length() == 0 || endWord.length() == 0 || beginWord.length() != endWord.length()) {
            return 0;
        }
        Set<String> dict = new HashSet<>(wordList);
        Queue<String> queue = new LinkedList<>();
        int current = 1;
        int future = 0;
        int level = 1;
        queue.offer(beginWord);
        
        while (!queue.isEmpty()) {
            current--;
            String str = queue.poll();
        for (int i = 0; i < beginWord.length(); i++) {
                    StringBuilder sb = new StringBuilder(str);
            for (char c = 'a'; c <= 'z'; c++) {
                sb.replace(i, i + 1, String.valueOf(c));
                String newStr = sb.toString();
                if (dict.contains(newStr)) {
                    if (newStr.equals(endWord)) {
                        return level + 1;
                    }
                    dict.remove(newStr);
                    queue.offer(newStr);
                    future++;
                }
            }
        }
            if (current == 0) {
                current = future;
                future = 0;;
                level++;
            }
        }
        return 0;
    }
}