0127 Word Ladder

Question

My Solution:

class Solution {
    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
        Set<String> beginSet = new HashSet<>();
        Set<String> endSet = new HashSet<>();
        beginSet.add(beginWord);
        endSet.add(endWord);
        Set<String> dict = new HashSet<>(wordList);
        if(!dict.contains(endWord)) return 0;
        return search(beginSet, endSet, dict, true, 1);
    }
    
    
    private int search(Set<String> beginSet, Set<String> endSet, Set<String> dict, boolean isForward, int cnt){
        if(beginSet.isEmpty() || endSet.isEmpty()) return 0;
        cnt++;
        dict.removeAll(beginSet);
        Set<String> nextSet = new HashSet<>();
        for(String str : beginSet){
            char[] chs = str.toCharArray();
            for(int i = 0; i < chs.length; i++){
                char c = chs[i];
                for(char j = 'a'; j <= 'z'; j++){
                    chs[i] = j;
                    String tmp = new String(chs);
                    if(!dict.contains(tmp)) continue;
                    if(endSet.contains(tmp)) return cnt;
                    nextSet.add(tmp);
                }
                chs[i] = c;
            }
        }
        return nextSet.size() > endSet.size() ? search(endSet, nextSet, dict, false, cnt) : search(nextSet, endSet, dict, true, cnt);
    }
}