TLE求助（悬关）

#include<bits/stdc++.h>
using namespace std;
string s,e,x,y,ru[11];
struct node{
    int val;
    string ch;
    bool operator<(node x)const{
        return val>x.val;
    }
    bool operator>(node x)const{
        return val<x.val;
    }
};
int ans=INT_MAX,cnt;
map< string,vector<string> >rules;
map< string,int >vis;
priority_queue<node>q;
void bfs(string s){
    vis[s]=true;
    q.push(node{0,s});
    while(!q.empty()){
        node now=q.top();q.pop();
        if(now.ch==e)ans=min(ans,now.val);
        for(int i=1;i<=cnt;i++){
            if(now.ch.length()<ru[i].length())continue;
            for(int j=0;j<=now.ch.length()-ru[i].length();j++){
//                cout<<j<<" "<<ru[i].length()+j<<" "<<now.ch.substr(j,ru[i].length())<<" "<<ru[i]<<endl;
                if(now.ch.substr(j,ru[i].length())==ru[i]){
                    string temp=now.ch;
                    for(int k=0;k<rules[ru[i]].size();k++){
                        temp.replace(j,ru[i].length(),rules[ru[i]][k]);
                        if(vis[temp]==1||now.val+1>=10)continue;
                        q.push(node{now.val+1,temp});
                        vis[temp]=1;
//                        cout<<now.ch<<"--->"<<temp<<endl;
                    }
                }
            }
        }
    }
    return;
}
int main(){
    cin>>s>>e;
    while(cin>>x>>y){
        ru[++cnt]=x;
        rules[x].push_back(y);
    }
    bfs(s);
    if(ans>=10)cout<<"NO ANSWER!"<<endl;
    else cout<<ans<<endl;
    return 0;
}