3325: Count Substrings With K-Frequency Characters I

Problem Statement

Given a string s and an integer k, return the total number of substrings of s where at least one character appears at least k times.

Example 1:

Input: s = "abacb", k = 2

Output: 4

Explanation:

The valid substrings are:

  • "aba" (character 'a' appears 2 times).
  • "abac" (character 'a' appears 2 times).
  • "abacb" (character 'a' appears 2 times).
  • "bacb" (character 'b' appears 2 times).

Example 2:

Input: s = "abcde", k = 1

Output: 15

Explanation:

All substrings are valid because every character appears at least once.

Constraints:

  • 1 <= s.length <= 3000
  • 1 <= k <= s.length
  • s consists only of lowercase English letters.

Code Solution