Overview In a distant country, a queen is very superstitious and does not like numbers with repeated digits like 77, 434 or 2121. Thus, she declares any number with repeated digits to be invalid. You have been appointed by Her Majesty to write a program that, given two integers a and b, determines how many valid numbers exist between a and b, inclusive. Examples: For a = 3 and b = 12, the answer is 9. For a = 12 and b = 34, the answer is 21. Requirements When developing your solution to this problem, ensure that your program conforms to the following requirements and assumptions: Name the source file containing the main function different digits.cpp. Implementation is written such that it is readable by other programmers. Use descriptive variable identifiers and comments where appropriate comments should explain things that are not obvious from the code). You cannot use string variables in this assignment. The input/output format should be exactly as follows. The input is given by two integers a and b such that 0 #include "functions.h