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 Python (judge verdict: Accepted)

#!/usr/bin/env python

from collections import deque
import itertools as it
import sys

sys.setrecursionlimit(1000000)

while True:
    S = raw_input()
    if S == '0':
        break
    m = [0 for i in range(11)]
    m[0] = 1
    diff = 0
    even = 1
    S = reversed(S)
    ans = 0
    for c in S:
        num = int(c)
        diff += num * even
        diff %= 11
        if num != 0:
            ans += m[diff]
        m[diff] += 1
        even *= -1
    print ans