魔改一波还是不对
搞不懂发生了什么
```cpp
#include<iostream>
#include<string>
#include<queue>
#include<unordered_map>
using namespace std;
int n,ans;
string A,B,a[10],b[10],fuck=" ";
struct node
{
string str;
int step;
};
unordered_map<string,bool>book;
queue<node>q;
string replace_n(string str,string&a,string&b,int n)//将str中第n次出现的字串a替换成b
{
int pos=0;
if(pos==-str.npos)return"NULL";
for(int i=1;i<=n;i++)
{
pos=str.find(a,pos+str.find(a));
if(pos==str.npos)return"NULL";
}
return str.replace(pos,a.size(),b);
}
int main()
{
cin>>A>>B;
A=" "+A;B=" "+B;
while(++n,cin>>a[n]>>b[n]);
q.push((node){A,0});
while(!q.empty())
{
node now=q.front(),to;
q.pop();
if(now.str==B)return cout<<now.step,0;
for(auto i=1;i<n;i++)
{
for(auto j=1;j<10;j++)
{
if(now.step<10&&replace_n(now.str,a[i],b[i],j)!="NULL")
{
to=(node){replace_n(now.str,a[i],b[i],j),now.step+1};
if(!book[to.str])
book[to.str]=true,q.push(to);
}
}
}
}
cout<<"NO ANSWER!";
// string aa="abcfffabadjs",bb="XxxX",cc="abc";
// if(aa.rfind(bb)!=aa.npos)cout<<aa.rfind(bb);
// else cout<<"fuck\n";
}
```
by NewSjf @ 2019-08-24 16:28:48
by Kiana_Kaslana @ 2019-09-27 22:22:23