Find first non-repeating character index

You are given two separate coding tasks. ## Task 1: First Unique Character Given a string `s` (lowercase/ASCII letters), return the **index of the first character that appears exactly once** in the string. If no such character exists, return `-1`. **Input:** `s` (string) **Output:** integer index (0-based) or `-1` **Examples** - `s = "leetcode"` → `0` (character `'l'`) - `s = "loveleetcode"` → `2` (character `'v'`) - `s = "aabb"` → `-1` --- ## Task 2: Highest Average Score You are given a list of student score records. Each record contains a `student_id` (string) and a `score` (integer). A student can appear multiple times. Compute the **average score per student** (mean of all that student’s scores), and return the **maximum average** across all students. **Input:** list of pairs `[(student_id, score), ...]` **Output:** the highest average (as a floating-point value or as an exact rational; specify your choice during the interview) **Example** Input: `[("a", 80), ("b", 90), ("a", 100)]` - avg(a) = (80 + 100) / 2 = 90 - avg(b) = 90 Output: `90` **Notes / Clarifications to ask:** - Should ties return just the value, or also the student id(s)? - How should rounding be handled if the average is not an integer?