int ladderLength(string beginWord, string endWord, unordered_set<string>& wordList) {
if (beginWord == endWord) return 1;
unordered_set<string> words1, words2;
words1.insert(beginWord);
words2.insert(endWord);
wordList.erase(beginWord);
wordList.erase(endWord);
return ladderLengthHelper(words1, words2, wordList, 1);
}
int ladderLengthHelper(vector<pair<string, int> >& start, vector<pair<string, int> >& end, unordered_set<string>& wordDict, unordered_map<string, bool>& sm, unordered_map<string, bool>& em) {
if (start.size() > end.size())
return ladderLengthHelper(end, start, wordDict, em, sm);
if (start.size() == 0)
return 0;
int size = start.size();
for (int i = 0; i < size; i++)
wordDict.erase(start[i].first);
for (int i = 0; i < size; i++) {
pair<string, int> cur = start.front();
start.erase(start.begin());
vector<string> strSet = findStrSet(cur.first, wordDict);
for (int j = 0; j < strSet.size(); j++) {
if (em[strSet[j]])
return cur.second + end.back().second;
sm[strSet[j]] = true;
start.push_back(make_pair(strSet[j], cur.second + 1));
}
}
return ladderLengthHelper(start, end, wordDict, sm, em);
}
int ladderLengthHelper(unordered_set<string>& words1, unordered_set<string>& words2,
unordered_set<string>& dict, int level) {
if (words1.empty()) return 0;
if (words1.size() > words2.size()) {
return ladderLengthHelper(words2, words1, dict, level);
}
unordered_set<string> words3;
for (auto it = words1.begin(); it != words1.end(); ++it) {
string word = *it;
for (char& c : word) {
char tmp = c;
for (c = 'a'; c <= 'z'; ++(c)) {
if (words2.find(word) != words2.end()) return level + 1;
else if (dict.find(word) != dict.end()) {
dict.erase(word);
words3.insert(word);
}
}
c = tmp;
}
}
return ladderLengthHelper(words2, words3, dict, level + 1);
}
int ladderLength(string beginWord, string endWord, unordered_set<string>& wordDict) {
if (beginWord == endWord)
return 1;
wordDict.insert(beginWord);
wordDict.insert(endWord);
unordered_map<string, bool> sm;
unordered_map<string, bool> em;
for (auto it = wordDict.begin(); it != wordDict.end(); it++) {
sm[*it] = false;
em[*it] = false;
}
sm[beginWord] = true;
em[endWord] = true;
vector<pair<string, int> > start;
vector<pair<string, int> > end;
start.push_back(make_pair(beginWord, 1));
end.push_back(make_pair(endWord, 1));
return ladderLengthHelper(start, end, wordDict, sm, em);
}
