First Missing Positive || Intuition + Example + Explanation || Must Do for Amazon

Video Description

Given an unsorted integer array nums, return the smallest missing positive integer. You must implement an algorithm that runs in O(n) time and uses constant extra space. Example 1: Input: nums = [1,2,0] Output: 3 Example 2: Input: nums = [3,4,-1,1] Output: 2 Example 3: Input: nums = [7,8,9,11,12] Output: 1