public class WordLadder

{

public static int FindLadders(string beginWord, string endWord, HashSet<string> wordList)

{

if (wordList == null || wordList.Count == 0)

{

return 0;

}

var queue = new Queue<string>();

queue.Enqueue(beginWord);

wordList.Remove(beginWord);

var res = 1;

char[] letters = new char['z' - 'a' + 1];

for (int i = 0; i < letters.Length; i++)

{

letters[i] = (char)((int)'a' + i);

}

while (queue.Count > 0)

{

int n = queue.Count;

for (int i = 0; i < n; i++)

{

var pop = queue.Dequeue();

foreach (var c in letters)

{

for (var j = 0; j < pop.Length; j++)

{

if (c != pop[j])

{

var tmp = pop.Substring(0, j) + c + pop.Substring(j + 1);

if (tmp.Equals(endWord))

{

return res + 1;

}

if (wordList.Contains(tmp))

{

queue.Enqueue(tmp);

wordList.Remove(tmp);

}

}

}

}

}

res += 1;

}

return 0;

}

}