next_positive.py

def solution(A):
    # sort the array of unique items 
    sorted_a = list(sorted(set(A)))

    # record the index of the last negative number or 0
    neg_index = 0

    for i in range(len(sorted_a)):
        if sorted_a[i] <= 0 :
            neg_index = i 


    # if no negatives, start loop at 0 
    if neg_index == 0:
        return find_next(sorted_a[1:])
            
        
    # if neg_index == len(arr) - meaning that all items are negative, return 1
    if neg_index == len(sorted_a):
        return 1

    

    # else split the array from where positives starts
    split_arr = sorted_a[neg_index+1: ]


    return find_next(split_arr)
        

def find_next(arr):
    if len(arr) == 0:
        return 1 

    i = 1 

    while i <= len(arr):
        curr = arr[i-1]

        if curr != i:
            return i

        next_item = curr 

        if i + 1 < len(arr):
            next_item = arr[i]

        # if they refer to the same item, then the highest is the next item
        if curr == next_item:
            return curr + 1 

        # if not, check that next-curr == 1 if > 1, then curr+1,
        if next_item - curr > 1:
            return curr + 1 

        i += 1


            
if __name__ == "__main__":
    a = [0,1,2,3,4,5,6,7,8,9,10,11,12]

    n = solution(a)
    print(n)