How should I practice First Missing Positive?

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

Is First Missing Positive associated with Microsoft?

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

First Missing Positive

Microsoft● HardFULLTIMEPHONE SCREEN

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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.