828. Count Unique Characters of All Substrings of a Given String (H)

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.

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".
Evey 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 <= 105

• s consists of uppercase English letters only.

Solution:

Similar as LC 42

https://www.youtube.com/watch?v=v0iZs3-_1c4

https://www.youtube.com/watch?v=eN8zATT702M https://leetcode.com/problems/count-unique-characters-of-all-substrings-of-a-given-string/discuss/1505263/Single-pass-O(n)-time-and-O(1)-space-solution-with-detailed-explanation/115166