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Amazon Online Assessment 2021 (OA) - Unique Character

There's an interesting experiment currently underway with a team that's working on enhancing the process of search queries; this depends on the placement area of the first unique character within a given search. An aspect of this experiment involves conducting tests to check how well the newly created queries are performing. Talking about a unique character, it can be defined as a character that only pops up once in a string; these characters are solely limited to lowercase English alphabets. To get into the specifics, the algorithm needs to identify and return the position of the first unique character appearing in a string; it's worth noting that this uses 1-based indexing. If a situation arises where there are no unique characters at all within a string, the system should return -1.

Relevant Amazon OA Problems:

Input & Output
Input
s — a string
Output
either the 1-based index or -1
Example
Input
s = statistics
Output
3
Explanation

The unique character are a, c among which a occurs first. Using 1-based indexing, it is at index 3.

Constraints
  • 1 <= length of s <= 10^5
  • The string s consists of lowercase English letters

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