写一个函数，返回不同的计数

题目描述：

# Write a function that will return the count of distinct
# case-insensitive alphabetic characters and numeric digits t
# hat occur more than once in the input string. The input
# string can be assumed to contain only alphabets (both uppercase and lowercase) and numeric digits.

我的解答：

def duplicate_count(text):
    t = str(text).lower()
    dic_1 = {}
    a = 0
    for i in t:
        dic_1[i] = t.count(i)
    for j in dic_1.keys():
        if dic_1[j] > 1:
            a += 1
    return a

更优解法：

def duplicate_count(s):
    return len([c for c in set(s.lower()) if s.lower().count(c) > 1])