first_recurring_charater

arr = [2,5,1,2,3,5,1,2,4]
arr2 = [2,1,1,2,3,5,1,2,4]
arr3 = [2,3,4,5]

def repeating_numbers(inp):
    seen = set()

    for i in inp:
        if i in seen:
            return i
        seen.add(i)
    return None

print(repeating_numbers(arr))