Find the first recurring character in a string

 Problem:

Given a string, return the first recurring character in it, or None if there is no recurring character.

For example, given the string "abdefgccad", return "c". Given the string "abcdefgh", return None.

 Solution1:

 def str_opr(s):
    for i,x in enumerate(s):
        if x in s[:i]:
            return x
    return None

print(str_opr('abdefgccad'))

Solution2:

def str_opr(s):
    lis = set()
    for x in s:
        if x in lis:
            return x
        lis.add(x)
    return None
print(str_opr('abdefgccad'))