Dealing with DSA

Problem: 3405. Count Arrays with K Matching Adjacent Elements📚 Topics: Combinatorics, DP, Modulo Math

💡 Key Insight:

→ Answer = m × C(n−1, k) × (m−1)^(n−1−k) % MOD

Where:

m is the choice for the first element

C(n - 1, k) is the number of ways to choose where equal pairs occur

(m - 1)^{n - 1 - k} handles diversity in remaining slots

🧠 Complexity:

→ Smart blend of choices + combinations + modular exponentiation

✅ Implemented in C++

📌 Time: O(k + log(mod) | Space: O(1)

🎯 Logic meets math. One problem at a time — let’s gooo! 🚀