Henry Baker wrote:
I programmed my current "level 1" solving ability (in Lisp, of course!), so that I could test it against a number of Sudoku puzzles. The idea is to come up with a uniform definition of level of difficulty.
Your definition is indeed the agreed-upon standard for "easy" sudoku. Most people phrase it as allowing two different rules: 1) If a certain square S can only hold one digit d, put d in S. 2) If a certain digit d can only show up in one square S of some 9-block region, put d in S. Your representation gives you rule 1 "for free" -- well, once you enforce the definitional "rule 0", that putting d in S means you eliminate d as a choice for all other squares in all regions containing S. I should point out that what Wayne Gould did to start the sudoku craze was precisely write a program that solved them according to a bunch of well-defined rules with a uniform definition of difficulty (and generated random ones to feed into the solver). The early sudoku analysis spent time trying to figure out precisely which solving rules Gould's program used, in which order and with which difficulty tags, based on the ratings that ran with his puzzles in major papers around the world. But the creation market soon became glutted with upstarts entirely lacking in standards, hence the situation as it is today. --Michael Kleber -- It is very dark and after 2000. If you continue you are likely to be eaten by a bleen.