{"id":482,"date":"2006-09-05T21:08:26","date_gmt":"2006-09-05T18:08:26","guid":{"rendered":"http:\/\/www.all-things-me.net\/blog\/archives\/2006\/09\/05\/defeating-sudoku-in-five-simple-steps"},"modified":"2007-10-21T15:04:35","modified_gmt":"2007-10-21T12:04:35","slug":"defeating-sudoku","status":"publish","type":"post","link":"https:\/\/www.all-things-me.net\/blog\/2006\/09\/05\/defeating-sudoku","title":{"rendered":"Defeating Sudoku in five simple steps"},"content":{"rendered":"

I, like many others, have taken a liking to Sudoku puzzles<\/a>. I started with some simple scanning techniques (examples 1-3) which worked with the easier puzzles. Angus Johnson’s Simple Sudoku<\/a> program has a delightful Help containing many strategies to solving a puzzle. I haven’t got the hang of (or memorised) the most advanced techniques but recently I finished even the “Ultimate Challenges” in two Sudoku books (about 200 puzzles each) with the following strategies that I’ve found the most effective — and enough.<\/p>\n

1. I always start a puzzle by looking at the smallest area possible which is the 3×3 square. I check the missing numbers starting from 1 and see if I can put a number anywhere.<\/p>\n

\"Sudoku<\/p>\n

2. After I’ve gone through each of the 9 small squares so many times that I can’t add numbers anymore, I check each horizontal row.<\/p>\n

\"Sudoku<\/p>\n

3. After horizontal rows don’t help, I check each vertical row.<\/p>\n

\"Sudoku<\/p>\n

4. I repeat steps 1-3 until I can’t add any numbers. Then I write down the “candidates” in each square. Often this reveals new numbers to add when a square has only one possible candidate.<\/p>\n

When the candidates are written down it’s easy to see pairs or small groups so I can strike out candidates in other squares. In the example there are three squares that have to contain the numbers 1,4, and 5 so I can discard them in the square that is outside the group. I do this scan on horizontal and vertical rows, too.<\/p>\n

\"Sudoku<\/p>\n

5. With the candidates in view it’s easy to find numbers to strike out when I go through the rows horizontally and vertically and notice that a number has to be contained in one of the 3×3 squares. Then I can strike out the number in the other 3×3 squares on the same row. Also, if a number is restricted to a 3×3 square and<\/em> a vertical or horizontal row, candidates can be struck out within the 3×3 square.<\/p>\n

In the example numbers 3, 6, and 9 have to be found on the first row so they can be struck out elsewhere in the second 3×3 square.<\/p>\n

\"Sudoku<\/p>\n

Before I learned the strategies 4 and 5 I had trouble finishing the tougher puzzles. I suppose I had thought of checking the pairs but not the larger groups.<\/p>\n

Perhaps next I should take on making<\/em> the puzzles because I tried that on Simple Sudoku<\/a> and couldn’t get a single one pass the check (= only one solution).<\/p>\n

Disclaimer: The examples are not trying to be realistic situations or solveable puzzles, they’re just diagrams.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

I, like many others, have taken a liking to Sudoku puzzles. I started with some simple scanning techniques (examples 1-3) which worked with the easier puzzles. Angus Johnson’s Simple Sudoku program has a delightful Help containing many strategies to solving a puzzle. I haven’t got the hang of (or memorised) the most advanced techniques but […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12,22],"tags":[],"class_list":["post-482","post","type-post","status-publish","format-standard","hentry","category-games","category-rants"],"_links":{"self":[{"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/posts\/482","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/comments?post=482"}],"version-history":[{"count":0,"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/posts\/482\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/media?parent=482"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/categories?post=482"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.all-things-me.net\/blog\/wp-json\/wp\/v2\/tags?post=482"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}