How to Solve Minimum Number of Operations to Make Word K-Periodic Problem

You are given a string word of size n, and an integer k such that k divides n. In one operation, you can pick any two indices i and j, that are divisible by k, then replace the substring of length k starting at i with the substring of length k starting at j. That is, replace the substring word[i..i + k - 1] with the substring word[j..j + k - 1]. Return the minimum number of operations required to make word k-periodic. We say that word is k-periodic if there is some string s of length k such that word can be obtained by concatenating s an arbitrary number of times. For example, if word == “ababab”, then word is 2-periodic for s = "ab".