2019 was a semiprime year with great contests and some notorious coincidences.

This year I setted some tie-break problems for CodeChef Long Challenge, probably the most interesting and with real life applications was Bacteria Synthesis about generating proteins from a genome using reversals. I also liked Coloring Triangulations which is about moving from one triangulation to another by flipping edges.

From the exact problems I liked LOVEMUFFIN which is a nice ad hoc game, and Pretty Boxes a flow that can be simulated with segment trees.

I also saw many interesting simple problems like Hit the Coconuts a puzzle that can be solved with a dp trick, and my brute forces Ada Rooks.