[Leetcode]--Word Ladder

public class Solution {
    public static int ladderLength(String start, String end,
            HashSet<String> dict) {
        int result = 0;
        
        if(dict.size() == 0){
            return result;
        }
        
        dict.add(start);
        dict.add(end);
        
        result = BFS(start, end, dict);
        
        return result;
    }
    
    public static int BFS(String start, String end, HashSet<String> dict){
        Queue<String> words = new LinkedList<String>();
        Queue<Integer> len = new LinkedList<Integer>();
        words.add(start);
        len.add(1);
        
        
        
        while(!words.isEmpty()){
            String word = words.poll();
            int l = len.poll();
            
            if(word.equals(end)){
                return l;
            }
            
            for(int i = 0; i< word.length(); i++){
                
                char[] arr = word.toCharArray();
                for (char c = ‘a‘; c <= ‘z‘; c++) {
                    
                    if(arr[i] == c){
                        continue;
                    }
                    
                    arr[i] = c;
                    
                    String str = String.valueOf(arr);
                    if(dict.contains(str)){
                        words.add(str);
                        len.add(l+1);
                        dict.remove(str);
                    }
                }
            }
            
        }
        
        return 0;
        
    }
}