Problem:
Problem H: Eleven Lover

Edward Leven loves multiples of eleven very much. When he sees a number, he always tries
to find consecutive subsequences (or substrings) forming multiples of eleven. He calls such
subsequences as 11-sequences. For example, he can find an 11-sequence 781 in a number 17819.

He thinks a number which has many 11-sequences is a good number. He would like to find out
a very good number. As the first step, he wants an easy way to count how many 11-sequences
are there in a given number. Even for him, counting them from a big number is not easy.
Fortunately, one of his friends, you, is a brilliant programmer. He asks you to write a program
to count the number of 11-sequences. Note that an 11-sequence must be a positive number
without leading zeros.

Input

The input is a sequence of lines each of which contains a number consisting of less than or equal
to 80000 digits.

The end of the input is indicated by a line containing a single zero, which should not be processed.

Output

For each input number, output a line containing the number of 11-sequences.

You can assume the answer fits in a 32-bit signed integer.

Sample Input

17819
1111
11011
1234567891011121314151617181920
0

Output for the Sample Input

1
4
4
38

Solution in C++11 (judge verdict: Accepted)

#include <iostream>

using namespace std;

int main(){
    string str;
    while(cin >> str,str!="0"){
        int n=str.size();
        int D[n];
        for(int i=0;i<n;i++){
            D[i]=((i&1)==1?-1:1)*(str[i]-'0');
        }
        int C[n]; fill(C,C+n,0);
        for(int i=0;i<n;i++){
            int sum=0;
            if(D[i]==0&&(i>0?C[i-1]:0)==0)continue;
            for(int j=i;j<n;j++){
                sum+=D[j];
                sum%=11;
                if(!sum){
                    if(D[i]==0){
                        C[j]+=(i>0?C[i-1]:0);
                    }else{
                        C[j]+=1+(i>0?C[i-1]:0);
                    }
                    break;
                }
            }
        }
        int count=0;
        for(auto& c:C)count+=c;
        cout << count << endl;
    }
    return 0;
}