Can Convolutional Neural Networks Crack Sudoku Puzzles?

Sudoku is a popular number puzzle that requires you to fill blanks in a 9X9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids contains all of the digits from 1 to 9. There have been various approaches to solving that, including computational ones. In this project, I show that simple convolutional neural networks have the potential to crack Sudoku without any rule-based postprocessing.

Requirements

NumPy >= 1.11.1
TensorFlow == 1.1

Background

To see what Sudoku is, check the wikipedia
To investigate this task comprehensively, read through McGuire et al. 2013.

Dataset

1M games were generated using generate_sudoku.py for training. I've uploaded them on the Kaggle dataset storage. They are available here.
30 authentic games were collected from http://1sudoku.com.

Model description

10 blocks of convolution layers of kernel size 3.

File description

generate_sudoku.py create sudoku games. You don't have to run this. Instead, download pre-generated games.
hyperparams.py includes all ajustable hyper parameters.
data_load.py loads data and put them in queues so multiple mini-bach data are generated in parallel.
modules.py contains some wrapper functions.
train.py is for training.
test.py is for test.

Training

STEP 1. Download and extract training data.
STEP 2. Run python train.py. Or download the pretrained file.

Test

Run python test.py.

Evaluation Metric

Accuracy is defined as

Number of blanks where the prediction matched the solution / Number of blanks.

Results

Ater a couple of hours of training, the training curve seems to reach the optimum.

I use a simple trick in inference. Instead of cracking the whole blanks all at once, I fill in a single blank where the prediction is the most probable among the all predictions. As can be seen below, my model scored 0.86 in accuracy. Details are avaiable in the `results` folder.

Level	Accuracy (#correct/#blanks=acc.)
Easy	47/47 = 1.00
Easy	45/45 = 1.00
Easy	47/47 = 1.00
Easy	45/45 = 1.00
Easy	47/47 = 1.00
Easy	46/46 = 1.00
Medium	33/53 = 0.62
Medium	55/55 = 1.00
Medium	55/55 = 1.00
Medium	53/53 = 1.00
Medium	33/52 = 0.63
Medium	51/56 = 0.91
Hard	29/56 = 0.52
Hard	55/55 = 1.00
Hard	27/55 = 0.49
Hard	57/57 = 1.00
Hard	35/55 = 0.64
Hard	15/56 = 0.27
Expert	56/56 = 1.00
Expert	55/55 = 1.00
Expert	54/54 = 1.00
Expert	55/55 = 1.00
Expert	17/55 = 0.31
Expert	54/54 = 1.00
Evil	50/50 = 1.00
Evil	50/50 = 1.00
Evil	49/49 = 1.00
Evil	28/53 = 0.53
Evil	51/51 = 1.00
Evil	51/51 = 1.00
Total Accuracy	1345/1568 = 0.86