Let's define a function countUniqueChars(s) that returns the number of unique characters on s. For example, calling countUniqueChars(s) if s = "LEETCODE " then "L ", "T ", "C ", "O ", "D " are the unique characters since they appear only once in s, therefore countUniqueChars(s) = 5. Given a string s, return the sum of countUniqueChars(t) where t is a substring of s. The test cases are generated such that the answer fits in a 32-bit integer. Notice that some substrings can be repeated so in this case you have to count the repeated ones too.