How should I practice First Missing Positive?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google phone screen problems in FastPrep.

Is First Missing Positive associated with Google?

FastPrep tags this as a Google phone screen coding practice problem when the problem catalog has that company and stage context.

Google● HardNEW GRADPHONE SCREEN

Given an unsorted integer array nums, return the smallest positive integer that does not appear in the array.

Your algorithm must run in O(n) time and use O(1) extra space, excluding the input array.

firstMissingPositive(nums: int[]) → int

nums = [1,2,0]return = 3

The positive values 1 and 2 are present, so 3 is the first missing positive.

nums = [3,4,-1,1]return = 2

The value 1 is present but 2 is absent.

nums = [7,8,9,11,12]return = 1

No value 1 appears.