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Day-170.cpp
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Day-170.cpp
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class Solution {
string beginWord;
string endWord;
vector<string>wordList;
unordered_set<string>present;
int min_step{INT_MAX};
unordered_map<string,vector<string>>graph;
unordered_map<string,int>visit_level;
unordered_set<string>completed;
void build(void){
queue<string>q;
q.push(beginWord);
int level = 0;
q.push("-1");
while (q.size() > 1) {
string word = q.front(); q.pop();
if (word == "-1") {
++level;
q.push(word);
continue;
}
completed.insert(word);
for (int i=0; i<word.size(); ++i) {
for (int j=0; j<26; ++j) {
string temp = word;
temp[i] = char(j+'a');
if (temp == endWord) {
min_step = level +2 ;
}
if (temp == word || present.find(temp) == present.end()) {
continue;
}
if (completed.find(temp) != completed.end()) {
continue;
}
if (completed.find(temp) == completed.end() && (visit_level[temp]==0
|| visit_level[temp] != visit_level[word])) {
visit_level[temp] = level+1;
graph[word].push_back(temp);
q.push(temp);
}
}
}
}
}
set<deque<string>>ans;
map<string,bool>visited;
void dfs(string current_node,deque<string>&c , int step) {
if (current_node == endWord) {
ans.insert(c);
return ;
}
if (step > min_step) {
return ;
}
for (auto&itr:graph[current_node]) {
c.push_back(itr);
if (!visited[itr]) {
visited[itr] = true;
dfs(itr , c , step+1);
visited[itr] = false;
}
c.pop_back();
}
}
public:
vector<vector<string>> findLadders(string beginWord, string endWord, vector<string>& wordList) {
for (auto&itr:wordList) {
present.insert(itr);
visited[itr] = false;
}
if (present.find(endWord) == present.end()) {
return {};
}
this->beginWord = beginWord;
this->endWord = endWord;
this->wordList = wordList;
build();
deque<string>c;
c.push_back(beginWord);
dfs(beginWord, c , 1);
vector<vector<string>>res;
for (auto it:ans) {
vector<string>s;
while (!it.empty()) {
s.push_back(it.front());
it.pop_front();
}
res.push_back(s);
}
return res;
}
};