Leetcode•Oct 31, 2026
Number of Good Ways to Split a String
Hazrat Ali
Leetcode
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").
Solution
var numSplits = function(s) {
const n = s.length;
const left = new Array(n).fill(0);
const right = new Array(n).fill(0);
let set = new Set();
for (let i = 0; i < n; i++) {
set.add(s[i]);
left[i] = set.size;
}
set.clear();
for (let i = n - 1; i >= 0; i--) {
set.add(s[i]);
right[i] = set.size;
}
let count = 0;
for (let i = 0; i < n - 1; i++) {
if (left[i] === right[i + 1]) {
count++;
}
}
return count;
};