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1525. Number of Good Ways to Split a String

Difficulty Topics

Description

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.

Solution

number-of-good-ways-to-split-a-string.py
class Solution:
    def numSplits(self, S: str) -> int:
        n = len(S)
        prefix = [None] * n
        suffix = [None] * n
        mp = set()
        res = 0

        for i in range(n):
            mp.add(S[i])
            prefix[i] = len(mp)

        mp.clear()

        for i in reversed(range(n)):
            mp.add(S[i])
            suffix[i] = len(mp)


        for i in range(1,n):
            res += prefix[i-1] == suffix[i]

        return res