Two Peaceful Knights — Solution & Editorial

Back to the Problem

All placements C(k², 2) minus attacking pairs: every 2×3 rectangle holds exactly two attacking arrangements, and there are 4(k−1)(k−2) such placements.

Complexity: O(N)

Watch out: k⁴/2 overflows 32 bits at k ≈ 300 — 64-bit throughout.