C - Long Beautiful Integer codeforces 1269C

#include<bits/stdc++.h>
using namespace std;
const int N=2E5+7;
char s[N],s1[N];
void solve()
{
    int n,k;
    cin>>n>>k;
    cin>>s;
    for(int i=0;i<k;i++){
        for(int j=i;j<n;j+=k){
            s1[j]=s[i];
        }
    }
    if(strcmp(s1,s)>=0){
        cout<<n<<endl;
        printf("%s",s1);
    }
    else {
        for(int i=k-1;i>=0;i--){
            if(s1[i]==‘9‘) {
                s1[i]=‘0‘;
            }
            else {
                s1[i]=s1[i]+1;
                break;
            }
        }
        for(int i=0;i<k;i++){
            for(int j=i;j<n;j+=k){
                s1[j]=s1[i];
            }
        }
        cout<<n<<endl;
        printf("%s",s1);

    }

}
int main(){
    solve();



    return 0;
}