How should I practice First Missing Positive?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Bloomberg LP onsite interview problems in FastPrep.

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FastPrep tags this as a Bloomberg LP onsite interview coding practice problem when the problem catalog has that company and stage context.

First Missing Positive

Bloomberg LP● HardNEW GRADONSITE INTERVIEW

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Problem statement

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.

Function

firstMissingPositive(nums: int[]) → int

Examples

Example 1

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

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

Example 2

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

The value 1 is present but 2 is absent.

Example 3

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

No value 1 appears.

Constraints

1 <= nums.length <= 100000.
-2^31 <= nums[i] <= 2^31 - 1.