#include<iostream>
#include<set>
#define ll long long
using namespace std;
int main()
{ ll iter,N,limit,T,K,i,count,indexa,indexb,flag;
cin>>T;
while(T--)
{
cin>>N;
string A,B;
cin>>A>>B;
set<ll>ai,bi;
flag=0;
for(i=0;i<N;i++){
if(B[i]!=A[i] && int(A[i])<int(B[i]))
{
flag=1;
break;
}
}
count=0;
for(i=0;i<N;i++){
if(A[i]!=B[i]){
count++;
}
}
ll counta=0,countb=0;
for(i=0;i<N;i++){
if(A[i]=='a')
counta++;
else if(A[i]=='b')
countb++;
}
if(flag==1 || counta==0 || countb==0){
cout<<-1<<"\n";
}
else if(count=0)
cout<<0;
else{
ll gotb=0;ll gota=0;
for(i=0;i<N;i++){
if(A[i]=='a' && gota==0)
{
gota=1;ai.insert(i);
}
else if(A[i]=='b' && gotb==0)
{
bi.insert(i);gotb=1;
}
}
for(i=0;i<N;i++){
if(B[i]!=A[i])
{
if(B[i]=='a')
ai.insert(i);
else if(B[i]=='b')
bi.insert(i);
}
}
cout<<2<<"\n";
cout<<ai.size()<<"\t";
for(ll x:ai)
cout<<x<<"\t";
cout<<"\n";
cout<<bi.size()<<"\t";
for(ll x:bi)
cout<<x<<"\t";
cout<<"\n";
}
}
return 0;
}
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