Sometimes I open the hint overview and see a Hidden Single. I go back to the puzzle, cannot find it, and think the app must be wrong. Then I ask for one more hint, see exactly where I missed it, and I am amazed at myself. Once you know it is there, it is easy to see.
That moment is why I made Grid9.
Getting stuck
I have always loved sudoku: the feeling when you start to read the puzzle, see the patterns, and see the logic of why it can only be that one digit. The feeling when you start to build a strategy — if this one is a 2, then that one cannot be a 2 — and the reasoning grows on several levels.
But you always reach a point where you get stuck. You know there is a solution, but you cannot see it. You look and look, you try different strategies, and you do not find the key, the breakthrough, as I call it, that more or less unlocks the whole puzzle.
Pencil, paper and a phone
I like solving sudoku best with a pencil and a book or a magazine, writing out the candidates and planning a strategy. A few years ago I started travelling for work, and like so many others I sat there with my phone. Of course I had downloaded a sudoku app, but it was either full of ads or hard to navigate, especially when it came to getting candidates into the puzzle.
I had also tried to learn new techniques by reading tutorials on how the different strategies work. But as usual it is hard to turn theory into practice. Even when you have understood the principle, you do not find the pattern in the puzzle when you are actually trying to solve it.
That was when I thought of an app that could help you, but in levels: a small first nudge in the right direction. If that is not enough, you can get one more hint.
Practising what I read
After reading about the different techniques, I realised that I wanted to try them, but on a puzzle where that technique was available right then. That is why I created Practice technique: you can read about a technique and then try it on a prepared puzzle.
At first I found it hard to get it right, even though the puzzle was prepared for the technique. I simply did not see the patterns. Frustrated, I added a Step by step guide to walk me through it. I always try to solve the puzzle myself first. When I cannot find the solution, I use Step by step to understand what I missed.
How I use it myself
I often look at just the hint overview, to see how many strategies are available. Most of the time I am stuck on something, and I can see that there is usually not just one possibility but several.
And on paper
I have solved many sudoku on paper, and I wanted the same chance to get help and to improve as I have in the app. That is why I added a mode where you can enter your own puzzle, the one you got stuck on.
I hope this app gives you many enjoyable moments.
— Joachim Hagedorn