Got an online assessment from a recruiter today for an iOS position

Format:

90 Minutes
3 Questions

Question 1
First non repeating character in a string

'abcdefghabcdefghz' would return 'z'

Question 2
Check whether a string is 'beautiful'.
A beautiful string is a string where the next lexographical character has less occurances than the previous character

'aabc' is beautiful since 2a, 1b and 1c
but
'aaabbbbcc' is not beautiful since 4b > 3a

Question 3

Check if a 9x9 Sudoku board is valid