127. Word Ladder
Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence frombeginWord 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 int LadderLength(string beginWord, string endWord, ISet<string> wordList) { var beginSet = new HashSet<string>(); var endSet = new HashSet<string>(); var visited = new HashSet<string>(); beginSet.Add(beginWord); endSet.Add(endWord); int res=1; while(beginSet.Count() >0 && endSet.Count() > 0) { if(beginSet.Count() > endSet.Count()) { var temp1 = beginSet; beginSet = endSet; endSet = temp1; } var temp = new HashSet<string>(); foreach( string word in beginSet) { var c = word.ToCharArray(); for(int i = 0;i<c.Length;i++) { var old = c[i];//keep the old value and unchange the string after the subloop for(char j = 'a';j<='z';j++) { c[i] = j; string dest = new string(c); if(endSet.Contains(dest)) return res+1; if(!visited.Contains(dest)&& wordList.Contains(dest)) { temp.Add(dest); visited.Add(dest); } } c[i] = old; } } beginSet = temp; res++; } return 0; }