CodeChef - Convert the String (CONVSTR)

  /****Bismillahir*Rahmanir*Rahim*******
 *         Riz1 Ahmed, CSE, LU.        *
 *          fb.com/riz1ahmed           *
 *  Code Start Time: 2020-05-30-20.52  *
 *************************************/
#include<bits/stdc++.h>
#define ll long long int
#define Fast ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define PrintV(v) for(auto i:v)cout<<i<<" ";puts("");
#define FOR(i,l,r) for(ll i=l;i<=r;i++)
using namespace std;
const ll Mod=1e9+7,MX=1e7,MN=LLONG_MIN;
void Print(ll a,ll b=MN,ll c=MN,ll d=MN) {
    printf("%lld",a);
    if (b!=MN) printf(" %lld",b);
    if (c!=MN) printf(" %lld",c);
    if (d!=MN) printf(" %lld",d);
    puts("");
}

int main(){
    ll n;
    char a[1005],b[1005];
    scanf("%*d");
    while(~scanf("%lld %s %s",&n,a,b)){
        ll pos[123], f=1 ,i;
        for (i=0;i<n && f;i++) if (a[i]<b[i]) f=0;
        for (i='a';i<='z' && f;i++) pos[i]=-1;
        for (i=0;i<n && f;i++) pos[a[i]]=i;

        vector< vector<ll> > v;
        vector<ll> let[123];
        for (i=0;i<n && f;i++)
            if (a[i]!=b[i]) let[b[i]].push_back(i);

        ///Comment it
//        for (i='a';i<='z' && f;i++)
//            if (let[i].size()){
//                printf("%c=",i);
//                for (auto it:let[i]) printf("%lld ",it);puts("");
//            }puts("");

        for (i='z';i>='a' && f;i--){
            if (let[i].size()){
                if (pos[i]==-1) {f=0;break;}
                ll x=pos[i];
                v.push_back(let[i]);

                for (auto it:let[i])
                    if (it==x){ x=-1; break;}
                if (x!=-1) v[v.size()-1].push_back(x);

//                for (auto it:let[i]) a[it]=i;
//                puts(a);
            }
        }
        if (!f) puts("-1");
        else{
//            printf("Ans is\n");
            printf("%d\n",v.size());
            for (i=0;i<v.size();i++){
                printf("%d ",v[i].size());
                for (auto it:v[i]) printf("%lld ",it);
                puts("");
            }
        }
    }
    return 0;
}