This function, find_missing_number, takes an unsorted array of unique integers that form a sequence and returns the nth missing number in that sequence, defaulting to the first missing number if nth is not specified. The smallest number in the sequence is assumed to be 1, and all numbers are positive.

1. Example 1:

This function, find_missing_number, takes an unsorted array of unique integers that form a sequence and returns the nth missing number in that sequence, defaulting to the first missing number if nth is not specified. The smallest number in the sequence is assumed to be 1, and all numbers are positive.

1. Example 1: