[Codility] MissingInteger

def solution(A):
    # write your code in Python 3.6
    A = list(filter(lambda x : x > 0 ,set(A)))
    
    if len(A) == 0 :
        return 1
    
    A.sort()
    m = min(1,A[0])
    s = m
    for a in A:
        if a == s:
            s += 1
            m = s
            continue
        else :
            return min(m,s)
    return s

others

class Solution: 
	def missingNumber(self, nums: List[int]) -> int:
    		max_num = max(nums) 
        	my_nums = set([num for num in range(max_num + 1)]) 
        	nums = set(nums) 
        	differ = my_nums - nums 

       		if len(differ) == 0: 
        		answer = max_num + 1 
        	else: 
        		answer = list(differ)[0] 
       		return answer

def solution(A):
    A.sort()
    min = 1
    for i in A:
        if i == min:
            min += 1
    return min