2262 - Total Appeal of A String\.

Hard

The appeal of a string is the number of distinct characters found in the string.

• For example, the appeal of "abbca" is 3 because it has 3 distinct characters: 'a', 'b', and 'c'.

Given a string s, return the total appeal of all of its substrings.

A substring is a contiguous sequence of characters within a string.

Example 1:

Input: s = "abbca"

Output: 28

Explanation: The following are the substrings of "abbca":

• Substrings of length 1: "a", "b", "b", "c", "a" have an appeal of 1, 1, 1, 1, and 1 respectively. The sum is 5.

• Substrings of length 2: "ab", "bb", "bc", "ca" have an appeal of 2, 1, 2, and 2 respectively. The sum is 7.

• Substrings of length 3: "abb", "bbc", "bca" have an appeal of 2, 2, and 3 respectively. The sum is 7.

• Substrings of length 4: "abbc", "bbca" have an appeal of 3 and 3 respectively. The sum is 6.

• Substrings of length 5: "abbca" has an appeal of 3. The sum is 3.

The total sum is 5 + 7 + 7 + 6 + 3 = 28.

Example 2:

Input: s = "code"

Output: 20

Explanation: The following are the substrings of "code":

• Substrings of length 1: "c", "o", "d", "e" have an appeal of 1, 1, 1, and 1 respectively. The sum is 4.

• Substrings of length 2: "co", "od", "de" have an appeal of 2, 2, and 2 respectively. The sum is 6.

• Substrings of length 3: "cod", "ode" have an appeal of 3 and 3 respectively. The sum is 6.

• Substrings of length 4: "code" has an appeal of 4. The sum is 4.

The total sum is 4 + 6 + 6 + 4 = 20.

Constraints:

• <code>1 <= s.length <= 10⁵</code>

• s consists of lowercase English letters.