# Simple sudoku backtrack algorithm.
to solve a sudoku puzzle starting from a partially filled board one can proceed as follows: Reading from left to right row by row, fill in the first available blank with the smallest digit 1. If it fails the increment by 1. If done, then move to the next blank and start trying from 1. If it all fails from 1 to 9, backtrack to previous filled position and increment that by one.
If we research a situation where there is no viable digit for the very first blank, then the puzzle is impossible.
There exists given sudoku entries where it has no contradictions but leads to no valid solves.