1525 Number of Good Ways to Split a String

You are given a string s.

A split is called good if you can split s into two non-empty strings sleft and sright where their concatenation is equal to s (i.e., sleft + sright = s) and the number of distinct letters in sleft and sright is the same.

Return the number of good splits you can make in s.

Example 1:

Input: s = "aacaba"
Output: 2
Explanation: There are 5 ways to split "aacaba" and 2 of them are good. 
("a", "acaba") Left string and right string contains 1 and 3 different letters respectively.
("aa", "caba") Left string and right string contains 1 and 3 different letters respectively.
("aac", "aba") Left string and right string contains 2 and 2 different letters respectively (good split).
("aaca", "ba") Left string and right string contains 2 and 2 different letters respectively (good split).
("aacab", "a") Left string and right string contains 3 and 1 different letters respectively.

Example 2:

Input: s = "abcd"
Output: 1
Explanation: Split the string as follows ("ab", "cd").

Constraints:

• 1 <= s.length <= 105
• s consists of only lowercase English letters.

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class Solution:
    def numSplits(self, s: str) -> int:
        r, l = Counter(s), set()
        res = 0
        for c in s:
            l.add(c)
            r[c] -= 1
            if r[c] == 0:
                del r[c]
            if len(r) == len(l):
                res += 1
        return res