Daily Challenge: JS-100 Find Smallest Missing Positive Integer (in C#)

JS-100.cs

/*
Find Smallest Missing Positive Integer
Write a function that finds the smallest positive integer
that is missing from an unsorted array of integers. 
Your function should run with an expected time complexity of O(n).

Example:
Input: [-1, 4, 2, 1, 9, 10]
Output: 3
*/

int[] array = { -1, 4, 2, 1, 9, 10 };

var hash = array.Where(a => a > 0 ).ToHashSet();
Enumerable.Range(1, Int32.MaxValue).First(e => hash.Add(e) ).Dump();