Given two words (start and end), and a dictionary, find the length of shortest transformation sequence from start to end, such that:
- Only one letter can be changed at a time
- Each intermediate word must exist in the dictionary
For example,
Given:
start = "hit"
end = "cog"
dict = ["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.
class Solution { public: int ladderLength(string start, string end, unordered_set<string> &dict) { unordered_set<string> add; add.insert(start); queue<string> q; q.push(start); int res=0; int levCurr=1,levNext=0; while(!q.empty()) { string s0=q.front(); q.pop(); levCurr--; for(int i=0;i<s0.size();i++) { for(char j='a';j<='z';j++) { if(s0[i]==char(j))continue; string s=s0; s[i]=char(j); if(s==end)return res+2; if(dict.find(s)!=dict.end()&&add.find(s)==add.end()) { add.insert(s); q.push(s); levNext++; } } } if(levCurr==0) { levCurr=levNext; levNext=0; res++; } } return 0; } };