C: The reference solution is not correct. An example from random_tests:

Expected 38, but got 39. 
Input: "FNBZVPFQOPKKHEXRQJ IHFJSCONRSL XOAVYFANIEMSBQOHWMGDULMADPCUGCUCQJNOOCQWGSDXXGDSTKVMKWMNKOHQFAIWJVZNX"

Both Python and JavaScript reference solutions return 39 for this input.

Ignore spaces altogether

If the string contains a number, return -1.

These side quests add nothing to the primary task, and should be removed. Uninteresting input preprocessing and validation have been done.

Testing with valid inputs only means no existing solutions will be invalidated.