Word Ladder

/*Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:

Only one letter can be changed at a time
Each intermediate word must exist in the word list
For example,

Given:
beginWord = "hit"
endWord = "cog"
wordList = ["hot","dot","dog","lot","log"]
As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

Note:
Return 0 if there is no such transformation sequence.
All words have the same length.
All words contain only lowercase alphabetic characters.
*/

public class Solution {
    public int ladderLength(String beginWord, String endWord, Set<String> wordList) {
        if(wordList == null || wordList.size() == 0 || beginWord.equals(endWord)){
            return 0;
        }
        Set<String> visit=new HashSet<String>();
        visit.add(beginWord);
        int count=1;
        Queue<String> queue=new LinkedList<String>();
        queue.add(beginWord);
        wordList.remove(beginWord);
        while(!queue.isEmpty()){
            int size=queue.size();
            for(int j=0;j<size;++j){
                String cur=queue.poll();
                for(int i=0;i<cur.length();++i){
                    for(char a='a';a<='z';++a){
                      if(a==cur.charAt(i)) continue;
                        String rep=replace(cur,i,a);
                        if(rep.equals(endWord)) return count+1;
                      if (visit.contains(rep)) {
                        continue;
                    }
                        if(wordList.contains(rep)){
                            queue.add(rep);
                            wordList.remove(rep);
                            visit.add(rep);
                        }
                    }
                }
            }
            count++;
        }
        return 0;
    }
    public String replace(String cur,int i,char a){
        char[] c=cur.toCharArray();
        c[i]=a;
        return new String(c);
    }
}