Total Appeal of A String

HardStringshashing

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

The **appeal** of a string is the number of **distinct** characters it contains. For example, the appeal of "abbca" is 3 (a, b, c). Given a string s of lowercase English letters, return the total appeal of all of its substrings, i.e. the sum of the appeal of every contiguous, non-empty substring. Substrings at different positions are counted separately even if they are equal. The result can exceed 32 bits for long strings, so return it as a 64-bit integer. Aim for O(n) time.

Examples

Input: s = "aba"
Output: 9
`a`, `b`, `a` have appeal 1 each; `ab`, `ba`, `aba` have appeal 2 each. 3 + 6 = 9.
Input: s = "zzz"
Output: 6
All 6 substrings contain only `z`, so each has appeal 1.

Constraints

  • `1 <= s.length <= 10^5`
  • `s` consists of lowercase English letters

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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