Count the number of Duplicates

Count the number of Duplicates

Write a function that will return the count of distinct case-insensitive alphabetic characters and numeric digits that 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.

Example

"abcde" -> 0 # no characters repeats more than once

"aabbcde" -> 2 # 'a' and 'b'

"aabBcde" -> 2 # 'a' occurs twice and 'b' twice (bandB)

"indivisibility" -> 1 # 'i' occurs six times

"Indivisibilities" -> 2 # 'i' occurs seven times and 's' occurs twice

"aA11" -> 2 # 'a' and '1'

"ABBA" -> 2 # 'A' and 'B' each occur twice

문자열에서 case insensitive하게 중복 문자가 몇개 존재하는지 구하는 문제, 나는 재귀함수를 이용해서 풀었다

def duplicate_count(text):
    text = text.lower()
    if text=='':
        return 0
    elif text[0] in text[1:]:
        return 1+duplicate_count(text[1:].replace(text[0],''))
    else :
        return duplicate_count(text[1:])