You are given a string word. A letter is called special if it appears both in lowercase and uppercase in word.
Return the number of special letters in word.
Example 1:
Input: word = "aaAbcBC"
Output: 3
Explanation:
The special characters in word are 'a', 'b', and 'c'.
Example 2:
Input: word = "abc"
Output: 0
Explanation:
No character in word appears in uppercase.
Example 3:
Input: word = "abBCab"
Output: 1
Explanation:
The only special character in word is 'b'.
Constraints:
1 <= word.length <= 50word consists of only lowercase and uppercase English letters."aaAbcBC" "abc" "abBCab"