Java

public class Solution {

public int ladderLength(String beginWord, String endWord, Set<String> wordList) {

Queue<String> q=new LinkedList<String>();

Set<String> visited=new HashSet<String>();

q.offer(beginWord);

visited.add(beginWord);

int distance=1;

int count=1;

while(count>0){

while(count>0){

//当前Level

char[] s=q.poll().toCharArray();

for(int i=0;i<s.length;i++){

char temp = s[i];

for(char c='a';c<'z';c++){

if(temp==c) continue;

s[i]=c;

String str= new String(s);

if(str.equals(endWord)) return distance+1;

if(str!=beginWord && wordList.contains(str)&&!visited.contains(str)){

q.offer(str);

visited.add(str);

}

}

s[i]=temp;

}

count--;

}

//计算下一个level

distance++;

count=q.size();

}

return 0;

}

}