Finish the method definition given below.
Sherlock considers a string to be valid if all characters of the string appear the same number of times.
It is also valid if he can remove just a single character at a single index in the string, and the remaining characters occur the same number of times.
Given an input string str, the method is_valid? should return true if the string is a valid Sherlock string and false if its not.
- For example, if str = "abc", the string is valid because the frequencies of characters are all the same.
- If str = "abcc", the string is also valid, because we can remove 1 "c" and have one of each character remaining in the string.
- However, if str = "abccc", the string is not valid, because removing one character does not result in the same frequency of characters.