1525. Number of Good Ways to Split a String

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.

 

Solutions

Solution: HashMap

• Time complexity: O(n)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {string} s
 * @return {number}
 */
const numSplits = function (s) {
  const current = new Set();
  const countMap = new Map();
  let result = 0;

  for (const char of s) {
    const count = countMap.get(char) ?? 0;

    countMap.set(char, count + 1);
  }

  for (const char of s) {
    const count = countMap.get(char);

    current.add(char);
    count - 1 ? countMap.set(char, count - 1) : countMap.delete(char);

    if (current.size === countMap.size) result += 1;
  }
  return result;
};