Count Permutable Substrings Matching UserID Pattern

amazon Programming Problem: User ID Matching Given two user ID strings userid1 and userid2, and an integer p. From userid2, select substrings every p characters apart with a length equal to userid1. Calculate how many such substrings can be permuted to match userid1. Input Description: Two strings userid1 and userid2 consisting of lowercase letters, both lengths not exceeding $10^5$. An integer p, such that $1 \leq p \le 100$. Output Description: An integer, representing the number of substrings that can be permuted to match userid1. Example 1: Input: userid1 = "abcd", userid2 = "abdccdccbdabda", p = 3 Output: 2 Example 2: Input: userid1 = "xyz", userid2 = "zyxzyzx", p = 1 Output: 3 Note that the solution should aim for efficiency. Example Input "abcd" "abdccdccbdabda" 3