}

```

###C++Version

*Method1: bi-directional bfs

```objectivec

classSolution {

intladderLength(stringbeginWord,stringendWord,vector<string>&wordList) {

unordered_set<string> set(wordList.begin(), wordList.end());

if(set.find(endWord)== set.end())return0;

set.erase(endWord);

unordered_set<string> first{beginWord}, second{endWord};

int len= endWord.length();

int step=0;

while(!first.empty()&&!second.empty()){

++step;

if(first.size()> second.size())

std::swap(first, second);

unordered_set<string> next;

for(string cur: first){

for(int i=0; i< len;++i){

char origin= cur[i];

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

cur[i]= c;

if(second.find(cur)!= second.end())return step+1;

if(set.find(cur)!= set.end()){

next.emplace(cur);

set.erase(cur);

}

cur[i]= origin;

}

}

}

std::swap(next, first);

}

return0;

}

};

```

###Conclusion

*How to choose dfs and bfs

1. bfs is designedfor shortest path question.