How to Solve Hiroimono Puzzles
Hiroimono, also known as Goishi Hiroi, which basically means “pick up Go stones,” was once a bar game in Japan. Go stones were laid out in a pattern on part of a board, and the player was challenged to pick up all the stones according to the following restrictions:
- Start with any stone and pick it up (in a printed puzzle, you will number the stones in the order you reach them, to show it has been picked up).
- Follow a horizontal or vertical line from the stone you just picked up to the next stone, and pick it up.
- Stones may not be skipped over – if you encounter it, you must pick it up.
- After picking up a stone, you may continue straight or turn 90 degrees. You may not reverse direction.
While you won’t always have this option, in easier puzzles, it is useful to look for stones which have only one path to reach them. At the beginning, one of them will likely be your first stone.
Because this is a simple example, there are only these two stones that are basically dead ends, so one will be the first stone, and the other will be the last.
Let’s see what the path looks like from the stone in the upper left first.
If we start with the green stone as the first one, there is only one stone that can be next, which I’ve marked as 2 here. Then, turning, we reach stone number 3, where we run into a problem.
If we turn to go up to the blue stone, we would then be stranded, as there would be no path from there to any other stone.
On the other hand, if we continue forward to the red stone, there would then be no stone left to reach the blue stone later. Because the goal is to pick up ALL the stones, the green stone cannot be our first one.
Again, because the two possibilities at the beginning were both dead ends with only one stone able to jump to them, they must be our two endpoints in this extremely simple example puzzle.
So, since the stone in the upper left was not the first stone in the sequence, it must be the last, and the stone that can reach it must be the next to last.
Going with the other stone, we easily find stone number 2 by going down, and because we know the one to its left is stone 7, then stone 3 must be to the right.
If we then continue straight to the red stone, we would strand the remaining stones after picking up stone 3. So Instead, we will turn to go up to the blue stone.
From here, the rest of the sequence is obvious, because the remaining stones form a rectangle. First up to the 4, then right to stone 5, down to 6, and now we can jump over the two stones we picked up earlier to reach stone 7, and finally up to stone 8.
This gives us the completed puzzle.
