Rules: Locate some blocks in the grid, having the size either 1×2 or 1×3. Each number in the grid should be part of a block, indicating the amount of the possible movements of the blocks. Blocks can only move in the direction of their short edge.
Background: Tren is one of 15th JPC Semifinal puzzles. This is a brilliant idea, I appreciate this puzzle’s idea owner! Similar as Easy as Japanese Sums, I gave the “Tren” name, because all things on the page were in Japanese language. You can see the original page where I met it for the first time.
I made several of this type for 24th HPC, OAPC, some national championships. But there is only one Tren puzzle for me: the one used in the Individual Finals of 18th WPC in Antalya. Probably most WPC solvers will remember it, especially Ulrich. In the Final round of 18th WPC, there was a Tren puzzle which was made by me, and the solution of that puzzle had a flaw. The Final round was canceled because of this. That puzzle has a unique solution, but the solution has an error. So judge compared Ulrich’s solution to this one, and Ulrich was penalized more than once although he had a correct solution. After that the Final round was repeated, and Ulrich became the champion.
– Edit: The inventor of the puzzle is Shinichi Aoki, and Japanese name is exactly “Parking”. This puzzle is based on Tokyo Parking (Rush Hour) by Nobuyuki Yoshigahara. So, each rectangle is a car and the puzzle is called “Parking”. Source of information: Takeya Saikachi