Systematic Sudoku (Sysudoku) is about human engineered techniques for solving Sudoku puzzles of all levels.
The most distinctive feature of Sysudoku is the actively solving nature of the candidate gathering phase, Sysudoku Basic. Instead of immediately deriving all possible candidates from given clues, as most Sudoku writing assumes, Sysudoku Basic uses clues, subsets, and unmarked strong links on an uncluttered grid to find clues and subsets.
The first Basic stage is called the bypass because, although it uses strong links, it bypasses the pencil marking except for subset candidates. Subsets are sets of n cells within a box or line reserved for n values. Like a clue, a subset bans candidates of its values elsewhere in its box or line. The idea is to work on an uncluttered grid, with only the candidates reserving cells.
Drag off About Sysudoku on the Menu Bar and click on Bypass & Tracing for a detailed illustration of the bypass on a Washington Post Saturday 6-star.
The second stage of Sysudoku Basic, box marking, records box slinks, the strong links defined by boxes. Two candidates form a strong link (or slink) when finding one to be false means the other one is true. In a box, if exactly two candidates have the same value, that’s a box slink. A new clue in a line with one of them makes the other true.
Instead of a linear or keypad style of positioning candidates within cells, Sysduoku uses pencil mark positions to mark slinks and subsets. The two candidates of a box slink see each other in matching positions at the top of two cells of the box. Row slink members are in lower left corners of two cells on the row; column slink members, in lower right corners of two cells of the column. There’s also a place for members of aligned row and column triples.
The box marking trace lists the boxes containig slinks and aligned triples of each value. Here’s the trace for the bypass example 6-star.
The box marking trace lists the boxes containing slinks and aligned triples of each value. Here’s the trace for the bypass example 6-star.
Line slinks, the strong links defined by exactly two candidates of a value in the line, are marked in a third stage (line marking), along with all remaining candidates.
Lines are filled efficiently by posting a fill string, a string of missing values, at the end of the line, and making a copy for each cell to be filled, removing from the copy each clue or line slink value seeing the cell being filled, and finally, adjusting the cell position of candidates to reflect new line or box slinks, and marking new bv cells. Lines are filled, fewest unfilled cells first. When lines in one direction are all filled, so are lines in the other direction, but line slinks remain to be marked in the unmarked lines.
For the line marking solution of the Washington Post 6-star, click Line Marking Solution off About Sysudoku on the Menu Bar.
Sysudoku Basic, with its strong link and bv marking, is preparation for advanced level puzzles. For puzzles that survive Sysudoku Basic, Sysudoku Advanced is a systematic progression of methods, beginning after line marking with easily spotted exclusive rectangles and bv chains known as remote pairs, and moving to bv patterns and chains, then to X-chains and fishing, then to AIC building, ALS chains, ALS_XZ, and pattern analysis. The progression is described in the Guide, and illustrated in the posts.
As it is with basic and follow up traces, the detailed graphic Sysudoku illustrations of advanced methods require investment, but accurately picture the level of the difficulty required.
Sysudoku Advanced also has a distinctive human engineering feature, a full version of Medusa coloring, which includes the strong link between the two candidates of a bv. Coloring marks slink networks called clusters, with long range strong links, acting as AIC shortcuts. All along the advanced path, coloring clusters can be started and built without interference with other methods. Clusters expand, past promising toward overwhelming, with each elimination and clue placement. Each cluster is a slink network of candidates across lines and boxes, half of which are true (that is, in the solution) and half, false. In office graphics, choose two colors for the cluster, and color the cluster pencil marks. Candidates of the two sides cooperate to remove candidates of the same value (traps). When any advanced move eliminates a candidate of one color, you can remove all candidates of that color and promote to clues all candidates of the alternate color. Sysudoku extends the ability to trap to candidates outside the cluster, an advantage called lite coloring.
Other distinctively innovative areas in Sysudoku Advanced: BARN, X maps in X-chains, fish and pattern analysis, systematic AIC building, and if I ever get it right, ALS mapping.
Most of the posts report solution paths of difficult puzzles as a way of rating published collections or reviewing Sudoku authors. Explanations in the posts are backed up by the Guide. Illustrated examples are taken from very limited sample puzzles selected from collection reviews and instructive books and sites, and newspapers, under “fair use” guidelines.
Sysudoku is free of ads and subscription fees, and offers free ©PowerPoint and ©Word templates for the puzzle grid, and for basic and advanced techniques seen in the posts, by email attachment, upon request to the address below.
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