Kropki Sudoku (from Polish, literally "dots"; also known as "Dots Sudoku") is the variation of the original sudoku. If absolute difference between two digits in neighboring cells equals 1, then they are separated by a white dot. If the digit is a half of digit in the neighboring cell, then they are separated by black dot. The dot between 1 and 2 can be either white or black.
The formats of sudoku files: