1525. Number of Good Ways to Split a String -------M

 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

A:

就是用了2个map 然后比较大小

class Solution {
public:
    int numSplits(string s) {
        int n = s.length();
        unordered_map<char,int> Left, Right;        
        for(int i =0;i<n;i++)
            Right[s[i]] += 1;
        
        int res = 0;
        for(int i = 0;i< n-1; i++){
            char ch = s[i];
            Left[ch]+=1;
            Right[ch] -= 1;
            if(Right[ch] == 0)
                Right.erase(ch);
            
            if(Left.size() == Right.size())
                res++;
        }
        return res;
    }
};