wordLadder

#include<iostream>

#include<vector>

#include<string>

#include<unordered_set>

#include<queue>

using namespace std;

int ladderLength(const string& start,const string& end,const unordered_set<string>& dict)

{
queue<string>cur,next;
unordered_set<string>visited;
auto state_is_target=[&](string& s){return s==end;};
auto next_state=[&](string& s){
vector<string>result;
string new_word(s);
for(int i=0;i<s.size();++i)
{
for(char c='a';c<='z';++c)
{
if(c==s[i])continue;
swap(c,s[i]);
new_word=s;
if((dict.count(new_word)||new_word==end)&&(!visited.count(new_word)))
{
result.push_back(new_word);
visited.insert(new_word);
}
swap(c,s[i]);
}
}
return result;
};
int level=0;
bool found=false;
cur.push(start);
while(!cur.empty()&&!found)
{
++level;
while(!cur.empty()&&!found)
{
string str=cur.front();
cur.pop();
const auto& new_states=next_state(str);
for(auto i:new_states)
{
next.push(i);
if(state_is_target(i))
{
found=true;
break;
}
}
}
swap(next,cur);
}
if(found)
return level+1;
else
return 0;

}

int main()

{
string start="hit";
string end="cog";
string a[]={"hot","dot","dog","lot","log"};
unordered_set<string>dict(a,a+5);
cout<<ladderLength(start,end,dict)<<endl;
return 0;

}