3639. Minimum Time to Activate String

You are given a string s of length n and an integer array order, where order is a permutation of the numbers in the range [0, n - 1]. Starting from time t = 0, replace the character at index order[t] in s with '*' at each time step. A substring is valid if it contains at least one '*'. A string is active if the total number of valid substrings is greater than or equal to k. Return the minimum