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 2 non-empty strings p and q where its concatenation is equal to s and the number of distinct letters in p and q are 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").

Example 3:

Input: s = "aaaaa"
Output: 4
Explanation: All possible splits are good.

Example 4:

Input: s = "acbadbaada"
Output: 2

Constraints:

• s contains only lowercase English letters.

• 1 <= s.length <= 10^5

class Solution {
    public int numSplits(String s) {
        int[] leftCount = new int[26];
        int[] rightCount = new int[26];
        int leftUnique = 0, rightUnique = 0;
        for (char c : s.toCharArray()) {
            if (rightCount[c - 'a'] == 0)
                rightUnique++;
            rightCount[c - 'a']++;
        }
        int ans = 0;
        for (char c : s.toCharArray()) {
            if (leftCount[c - 'a'] == 0)
                leftUnique++;
            if (rightCount[c - 'a'] == 1)
                rightUnique--;
            rightCount[c - 'a']--;
            leftCount[c - 'a']++;
            if (leftUnique == rightUnique)
                ans++;
        }
        return ans;
    }
}