41-First-Missing-Positive.py

class Solution:
    def firstMissingPositive(self, nums: List[int]) -> int:
        A = nums
        for i in range(len(A)):
            if A[i] < 0:
                A[i] = 0
            
        for i in range(len(A)):
            val = abs(A[i])
            if 1 <= val <= len(A):
                if A[val - 1] > 0:
                    A[val - 1] *= -1
                elif A[val - 1] == 0:
                    A[val - 1] = -1 * (len(A) + 1)
        
        for i in range( 1, len(A)+ 1):
            if A[i -1] >= 0:
                return i
        
        return len(A) + 1
        
    def firstMissingPositive_2(self, nums: List[int]) -> int:
        new = set(nums)
        i = 1
        while i in new:
            i += 1
        return i