# Problem Definition

## Description

Given an unsorted integer array, find the first missing positive integer.

Example:

Given

[1,2,0] return 3,
[3,4,-1,1] return 2,
[-8, -7, -6] returns 1

Your algorithm should run in O(n) time and use constant space.

## Notes

1. [Geeks for Geeks - Find the smallest positive number missing from an unsorted array | Set 1](https://www.geeksforgeeks.org/find-the-smallest-positive-number-missing-from-an-unsorted-array/)