First Missing Positive – Leetcode Python

LeetCode has a Hard coding Problem in Its' Algorithm Section "First Missing Positive". Today We are going to solve this problem.

Question
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.
Examples
Input: nums = [1,2,0]
Output: 3
Input: nums = [3,4,-1,1]
Output: 2
Input: nums = [7,8,9,11,12]
Output: 1
Constraints:
1 <= nums.length <= 5 * 105
-231 <= nums[i] <= 231 - 1

Solution to First Missing Positive
The Skeleton Code given by LeetCode is
class Solution(object):
def firstMissingPositive(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
Complete Solution:
visit https://hecodesit.com/first-missing-positive-leetcode-python/