Digit Sum Spoj

#include<bits/stdc++.h>
using namespace std;
#define ll long long int
ll dp[18][2] ;
ll couunt(string s,int n,bool tights){
    if(tights==0){
        return (pow(10,n)+0.1);
    }
 
    if(n==0){
        return 1;
    }
 
    int ub=tights?(s[s.length()-n]-'0'):9;
    ll ans=0;
    for(ll i=0;i<=ub;i++){
        ans+=couunt(s,n-1,(tights&&(i==ub)));
    }
 
    return ans;
}
ll solve(string s,int n,bool tights){
    if(n==0){
        return 0;
    }
    if(dp[n][tights]!=-1){
        return dp[n][tights];
    }
    int ub=tights?(s[s.length()-n]-'0'):9;
    ll ans=0;
    for(ll i=0;i<=ub;i++){
        ans+=i*couunt(s,n-1,(tights&&(i==ub)));
        ans+=solve(s,n-1,(tights&(i==ub)));
    }
 
    return dp[n][tights]=ans;
}
int main(){
    ll t;
    cin>>t;
    while(t--){
        ll L,R;
        cin>>L>>R;
       if(L!=0){
        L--;
       }
 
        string l=to_string(L);
        string r=to_string(R);
        memset(dp,-1,sizeof dp);
        ll fr=solve(r,r.length(),1);
        memset(dp,-1,sizeof dp);
        ll fl=solve(l,l.length(),1);
 
        cout<<(fr-fl)<<endl;
    }
}