public class Solution
extends Object
828 - Count Unique Characters of All Substrings of a Given String\.
Hard
Let's define a function `countUniqueChars(s)` that returns the number of unique characters on `s`.
* For example 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 <= 10`5
* `s` consists of uppercase English letters only.