单词最短路径

Input:
beginWord = "hit",
endWord = "cog",
wordList = ["hot","dot","dog","lot","log","cog"]

Output: 5

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

public int ladderLength(String beginWord,String endWord,List<String> wordList){
        wordList.add(beginWord);
        int start = wordList.size()-1;
        int end = 0;
        while(end<wordList.size()&& !wordList.get(end).equals(end)){
            end++;
        }
        if (end == wordList.size()){
            return 0;
        }
        List<Integer>[] graphic = buildGraphic(wordList);
        return getShortestPath(graphic,start,end);
    }
    
    private List<Integer>[] buildGraphic(List<String> wordList){
        int N = wordList.size();
        List<Integer>[] graphic = new List[N];
        for(int i=0;i<N;i++){
            graphic[i] = new ArrayList<Integer>();
            for(int j=0;j<N;j++){
                if(isConnect(wordList.get(i),wordList.get(j))){
                    graphic[i].add(j);
                }
            }
        }
        return graphic;
        
    }
    
    private boolean isConnect(String s1,String s2){
        int diffCnt = 0;
        for(int i=0;i<s1.length()&&diffCnt<=1;i++){
            if(s1.charAt(i)!=s2.charAt(i)){
                diffCnt++;
            }
        }
        return diffCnt == 1;
    }
    
    
    private int getShortestPath(List<Integer>[] graphic,int start,int end){
        Queue<Integer> queue = new LinkedList<Integer>();
        boolean[] marked = new boolean[graphic.length];
        queue.add(start);
        marked[start] = true;
        int path = 1;
        while(!queue.isEmpty()){
            int size = queue.size();
            path++;
            while(size-->0){
                int cur = queue.poll();
                for(int next:graphic[cur]){
                    if(next == end){
                        return path;
                    }
                    if(marked[next]){
                        continue;
                    }
                    marked[next] = true;
                    queue.add(next);
                }
            }
        }
        return 0;
    }