First Missing Positive

Hard
Description:

Given an unsorted integer array nums, return the smallest positive integer that is not present in nums.

You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space.

Example 1:
Input: nums = [1,2,0]
Output: 3
Explanation: The numbers in the range [1,2] are all in the array.

Input Format:

A single line containing space-separated integers representing the array nums.

Output Format:

A single integer — the smallest missing positive number.

Tags:
Array Hashing Cyclic Sort
Sample Input:
3 4 -1 1
Sample Output:
2