Codeforces: 260A. Adding Digits

The problem is from codeforces: http://www.codeforces.com/problemset/problem/260/A

This problem looks difficult at the first glance because of the input ranges are large for the given three integers. Using bruteforce to print all possibilities/combination is difficult, but the problem states that only print one possibility is enough.

Therefore, it is only needed to loop ten possibilities (0 to 9) on the right of the number a to check if it is divisible by number b. If yes, we just need to print a, followed by this digit and n – 1 times of zeros because this number is also divisible by b.

If none combination of the number a * 10 + x where x is from 0 to 9, divisible by b, we just print -1.

#!/usr/bin/env python

a, b, n = map(int, raw_input().split())

a *= 10
for _ in xrange(10):
    if (a + _) % b == 0:
        print str(a + _) + "0" * (n - 1)
        exit()

print -1

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