Author: Anurag Sahay
Enter all the given digits (A,B,C) into the grid so that in every row and every column each digit appears exactly once. Some cells will remain empty. When following the spiral from the outside to the inside the digit sequence 1, 2, C ... A, B, C must repeat. Digits outside show the first visible digit in the corresponding direction.
Grid control: Click at a cell reveals the value chooser. Click at the selected value changes the state of the cell. More details about grid control are at the help page.