Solve string and hashmap interview tasks

Coding questions (solve both)

1) First non-repeating character

Given a string s, return the first character that appears exactly once in the string.

• If no such character exists, return an empty value (e.g., "") or a special marker such as None/null.

Input: s (string)

Output: the first non-repeating character (or empty marker)

Constraints (typical):

• 1 <= len(s) <= 10^5
• s may contain letters (assume ASCII unless stated otherwise)

2) Best average score

You are given a list of score records. Each record contains a name (string) and a score (integer).

Return the highest average score among all names.

• A person may appear multiple times; their average is the mean of their scores.
• You may assume each person has at least one score.
• Specify how you handle rounding (e.g., return a floating-point number, or return an exact rational/decimal).

Input: records = [(name1, score1), (name2, score2), ...]

Output: the maximum average across names

Constraints (typical):

• 1 <= len(records) <= 10^5
• score can be negative or positive (state assumption if you restrict it)