Count Unique Characters of All Substrings of a Given String
Let's define a function countUniqueChars(s) that returns the number of unique characters in s.
Let's define a function countUniqueChars(s) that returns the number of unique characters in s.
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.
Example 1
Input: s = "ABC"
Output: 10
Explanation: All possible substrings are: "A","B","C","AB","BC" and "ABC". Every substring is composed with only unique letters. Sum of lengths of all substring is 1 + 1 + 1 + 2 + 2 + 3 = 10
Example 2
Input: s = "ABA"
Output: 8
Explanation: The same as example 1, except countUniqueChars("ABA") = 1.
Example 3
Input: s = "LEETCODE"
Output: 92
Constraints
- 1 <= s.length <= 10^5
- s consists of uppercase English letters only.
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