"Find the number" puzzle
I'm sorry, but the best solution to this problem has to be a logic solution, not a code solution. There are only 2 digits that, when multiplied by 3, have the same last digit... 0, and 5. So, 0+0+0 is 0, and 5+5+5 is 15.

Since C cannot be 0, it means that C can only be 5. Now, if C is 5, and we know that there is a 'carry' of 1 in to the tens column, it means we need to find a number other than 5 that when added together 3 times ends in a 4.

There is only one value that does that, 8. 8 + 8 + 8 is 24, and with the carry of 1, we have 25 (and a carry of 2 in to the 100's column).

So, now we need a digit that sums three times to 3, and that's 1.

There is only one possible solution where ABC + ABC + ABC is CCC, and that's 185. It can be deduced using logic alone, and brute-forcing it is overkill.