0127. Word Ladder

class Solution {
    public boolean trans(String s1, String s2){
        if(s1.length() != s2.length()) return false;
        int sum = 0;
        for(int i = 0; i < s1.length(); i++){
            if(s1.charAt(i) != s2.charAt(i))
                sum += 1;
            if(sum == 2) return false;
        }
        return true;
    }
    
    public int ladderLength(String beginWord, String endWord, List<String> wordList) {
        int res = 1;
        LinkedList<String> qu = new LinkedList<>();
        qu.add(beginWord);
        while(!qu.isEmpty()){
            LinkedList<String> newQu = new LinkedList<>();
            boolean flag = false;
            while(!qu.isEmpty()){
                String top = qu.poll();
                if(top.equals(endWord))
                    return res;
                for(int i = 0; i < wordList.size();){
                    if(trans(top, wordList.get(i))){
                        newQu.add(wordList.get(i));
                        wordList.remove(i);
                        flag = true;
                    }
                    else i++;
                }
            }
            if(flag){
                res += 1;
                qu = newQu;
            }
            else return 0;
            
        }
        return 0;
    }
}