}

```

### C++ Version

* Method 1: bi-directional bfs

```objectivec

class Solution {

public:

int ladderLength(string beginWord, string endWord, vector<string>& wordList) {

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

if(set.find(endWord) == set.end()) return 0;

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);

}

return 0;

}

};

```

### Conclusion

* How to choose dfs and bfs

1. bfs is designed for shortest path question.