Word Ladder
Given two words (beginWord and endWord), and a dictionary, find the length of shortest transformation sequence from beginWord to endWord, 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) {
if(start.size() != end.size()) return 0;
if(start.empty() || end.empty()) return 0;
queue<string> path;
path.push(start);
int level = 1;
int count = 1;
dict.erase(start);
while(dict.size() >0 && !path.empty()) {
string curword = path.front();
path.pop();count--;
for(int i = 0; i < curword.size(); i++) {
string tmp = curword;
for( char j = 'a'; j <= 'z';j++){
if(tmp[i] == j) continue;
tmp[i] =j;
if(tmp == end) return level+1;
if(dict.find(tmp) != dict.end()) path.push(tmp);
dict.erase(tmp);
}
}
if(count == 0) {
count = path.size();
level ++;
}
}
return 0;
}
};
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