gcc [filename].c -o out
time ./out [input file] [output file]
Originally from here. The file will be on the format:
<length>
<sudoku#1>,<solution#1>
<sudoku#2>,<solution#2>
...
<sudoku#n>,<solution#n>
To check solutions:
md5sum [filename]
MD5:
easy.txt 3cb465ef6077c4fcab5bd6ae3bc50d62
hard.txt 41704fd7d8fd0723a45ffbb2dbbfa488