Word Ladder

Given two words (start and end), and a dictionary, find the length of shortest transformation sequence from start to end, such that:

1. Only one letter can be changed at a time
2. Each intermediate word must exist in the dictionary

For example,

Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]

As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

public class Solution {
    public int ladderLength(String start, String end, HashSet<String> dict) {
        if(dict.size()==0)
            return 0;
        Queue<String> queue = new LinkedList<String> ();
        Queue<Integer> len = new LinkedList<Integer> ();
        dict.add(start);
        dict.add(end);
        queue.offer(start);
        len.offer(1);
        while(!queue.isEmpty()){
            String s = queue.poll();
            int l = len.poll();
            if(s.equals(end)) return l;
            for(int i=0;i<s.length();i++){
                char[] chars = s.toCharArray();
                for(char c='a';c<='z';c++){
                    if(c!=chars[i]){
                        chars[i]=c;
                        String temp = new String(chars);
                        if(dict.contains(temp)){
                            len.offer(l+1);
                            queue.offer(temp);
                            dict.remove(temp);
                        }
                    }
                }
            }
        }
        return 0;
    }
}