Review: Disctrail for iPhone and iPad

Disctrail by the Swedish Knappra AB is an interactive version of a lesser-known traditional Japanese puzzle called Goishi Hiroi or Hiroimono.

Compared to most of the puzzle games available on the App Store, Goishi Hiroi is fiercely unintuitive, and it had me stumped initially. It took a lot of practice to make it finally click and be able to solve the puzzle without feeling I was moving at random.

The basic rule of the puzzle is: find a continuous path that connects all the discs. At every step, you can move to the closest available disc in one of the four main directions, but you can't go back in the direction where you came from.

The first uncommon thing is that the path can intersect itself, like this:

Where things get really interesting is what happens when you pass over the same disc twice.

The traditional Goishi Hiroi would be played by putting stones on a Go board and picking them up in sequence, so by the time you'd pass again over the same spot, the stone would no longer be there.
This means that a disc can be the endpoint of a path segment only the first time you pass over it; the following times you can only pass over it as if it wasn't there, so there needs to be another disc on the opposite side.

One thing that I missed initially is that you don't need to tap each disc to create the path: you can simply draw it swiping your finger, which feels more intuitive. If you make a mistake, you can also wind back in the same way.

And many mistakes you will make. The intersections make this puzzle unintuitive, and as the grids get more complicated, the path will cross itself multiple times, making it difficult to picture it out in your head.

Note that because of how the intersections work, the solution is in general not reversible. For example in the puzzle above, if you started from the 14 and attempted to follow the path backwards, you'd use all the discs in the right column on the first pass, and would not be able to move back over it after the 11.

I believe most puzzles have a unique solution, though there are some that have multiple ones, like this one.

Deviating from the traditional rules, some puzzles use discs of two colors, which you must alternate between. This is not surprising since Go stones have two colors so it's a natural extension to use both. This blog post suggests the same thing.

In a sense this makes things easier because it reduces possibilities, but it also makes things harder because you may need to take a more tortuous path in order to respect the color rule.

Further deviating from the traditional rules, and departing even from the Go setting, some puzzles use three colors, which you need to cycle through. On the left of the screen is a reminder of the order to follow.
Initially I thought this was a new mode introduced by this game, but then I found the same kind of puzzles on the Danish website kalkulu.dk.

In some puzzles, the game will help you by indicating from which disc the path should start. This happens a bit randomly, i.e. you'll solve several puzzles without this help, and then it will appear again. I would have preferred to see a clear cut, with easy puzzles showing the hint and later ones not showing it.

Most puzzles have a random layout, but some are aestethically pleasing. I liked this one shaped like a torii. I wonder if it might be a traditional Goishi Hiroi layout.

The game comes with 16 free puzzles, then two additional packs of 48 puzzles each, unlockable through in app purchases.

The 16 free puzzles are definitely not enough to get a full taste of the game. After playing all of them, I was still confused by the rules, and finding the solution felt like pure trial and error in some cases. Only after getting about two thirds into the Green pack, I really started to appreciate the solving process.

I haven't found a way to solve all the puzzles by only using strict logic deductions, but logic can be used to exclude many possibilities that wouldn't allow to complete the path. Solving these puzzles is a bit of an art, and there are a few recurring tricks which one should learn with some practice.

The difficulty definitely increases while progressing, and things start to get tricky in the Yellow pack, which makes all the more rewarding to find the solution.

One thing that annoys me and which I don't think fits this kind of game is that after solving a puzzle you are given a stars rating which depends exclusively on the time it took you to find the solution. So if you think your moves carefully to find the solution on the first attempt without making any mistake, you'll invariable score just 1 star, which is a bit unfair.
Want to fix that? Just tap replay and repeat the solution as fast as you can. It becomes just a game of dexterity.

At the time of writing, the Green pack is free, so definitely download this game now and unlock that pack while the offer lasts. If you are confused after the first few puzzles, don't be put off and persevere. You will get it eventually.

Summary

Nontrivialness	★★★★☆
Logical Reasoning	★★★★☆
User Interface	★★★★☆
Presentation	★★★★☆
Loading Time	★★★★☆
Saves Partial Progress	✘
Status Bar	✘

©2013 Nicola Salmoria. Unauthorized use and/or duplication without express and written permission is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Nicola Salmoria and nontrivialgames.blogspot.com with appropriate and specific direction to the original content.