//double bfs: search from both start and end
int ladderLength(string start, string end, unordered_set<string> &dict) {
if (valid(start,end)){return 2;}
struct node{
string str;
int lev;
node(string s,int l):str(s),lev(l){}
};
queue<node>q;
queue<node>rq;
map<string,bool>mark;
map<string,bool>rmark;
for (auto it=dict.begin();it!=dict.end();it++){
mark[*it]=false;
rmark[*it]=false;
}
int level=1;
int rlevel=1;
q.push(node(start,1));
rq.push(node(end,1));
while (!q.empty() && !rq.empty()){
if (q.size()<rq.size()){
while (!q.empty() && q.front().lev==level){
vector<string> l = findDict(q.front().str,dict);
for (auto it=l.begin();it!=l.end();it++){
if (!mark[*it]){
mark[*it]=true;
if (rmark[*it]){return q.front().lev+rq.back().lev;}
q.push(node(*it,level+1));
}
}
q.pop();
}
level++;
}else{
while (!rq.empty() && rq.front().lev==rlevel){
vector<string> lr = findDict(rq.front().str,dict);
for (auto it=lr.begin();it!=lr.end();it++){
if (!rmark[*it]){
rmark[*it]=true;
if (mark[*it]){return rq.front().lev+q.back().lev;}
rq.push(node(*it,rlevel+1));
}
}
rq.pop();
}
rlevel++;
}
}
return 0;
}
int ladderLength(string start, string end, unordered_set<string> &dict) {
// Note: The Solution object is instantiated only once and is reused by each test case.
if (valid(start, end)) return 2;
queue<node> q;
queue<node> rq;
map<string, bool> mark;
map<string, bool> rmark;
for(auto it=dict.begin(); it!= dict.end(); it++){
mark[*it] = false;
rmark[*it] = false;
}
int level = 1;
int rlevel = 1;
q.push(node(start,1));
rq.push(node(end,1));
while(!q.empty() & !rq.empty()){
if (q.size()<rq.size()){
while (!q.empty() && q.front().lev==level){
vector<string> l = findDict(q.front().str,dict);
for (auto it=l.begin();it!=l.end();it++){
if (!mark[*it]){
mark[*it]=true;
if (rmark[*it]){return q.front().lev+rq.back().lev;}
q.push(node(*it,level+1));
}
}
q.pop();
}
level++;
}else{
while (!rq.empty() && rq.front().lev==rlevel){
vector<string> lr = findDict(rq.front().str,dict);
for (auto it=lr.begin();it!=lr.end();it++){
if (!rmark[*it]){
rmark[*it]=true;
if (mark[*it]){return rq.front().lev+q.back().lev;}
rq.push(node(*it,rlevel+1));
}
}
rq.pop();
}
rlevel++;
}
}
return 0;
}
