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Some hobbyists have developed computer programs that will solve Sudoku puzzles using a backtracking algorithm, which is a type of brute force search. [3] Backtracking is a depth-first search (in contrast to a breadth-first search), because it will completely explore one branch to a possible solution before moving to another branch.
The four cells in the top right cage (totaling 15) can only include one of 1, 3, 7, or 9 (if at all) because of the presence of 1, 3, 7, and 9 in the top right hand nonet. If any one of 1, 3, 7, or 9 is present then this must be the lone square in the nonet below. Therefore, these 4 cells are one of 1+2+4+8 or 2+3+4+6.
Another variant on the logic of the solution is "Clueless Sudoku", in which nine 9×9 Sudoku grids are each placed in a 3×3 array. The center cell in each 3×3 grid of all nine puzzles is left blank and forms a tenth Sudoku puzzle without any cell completed; hence, "clueless". [24] Examples and other variants can be found in the Glossary of ...
The general problem of solving Sudoku puzzles on n 2 ×n 2 grids of n×n blocks is known to be NP-complete. [8] A puzzle can be expressed as a graph coloring problem. [9] The aim is to construct a 9-coloring of a particular graph, given a partial 9-coloring. The Sudoku graph has 81 vertices, one vertex for each cell.
A Sudoku variant with prime N (7×7) and solution. (with Japanese symbols). Overlapping grids. The classic 9×9 Sudoku format can be generalized to an N×N row-column grid partitioned into N regions, where each of the N rows, columns and regions have N cells and each of the N digits occur once in each row, column or region.
It is particularly useful for efficiently implementing backtracking algorithms, such as Knuth's Algorithm X for the exact cover problem. [1] Algorithm X is a recursive , nondeterministic , depth-first , backtracking algorithm that finds all solutions to the exact cover problem.
Thomas Snyder (born c. 1980) [1] is an American puzzle creator and world-champion sudoku and logic puzzle solver. He is the first person to win both the World Sudoku Championship (3 times) and the World Puzzle Championship. Snyder writes a puzzle blog as Dr. Sudoku. [2]
The channel has produced nine Sudoku apps based on Sudoku variants: Classic, Chess, Miracle, Sandwich, Thermo, Killer, Arrow, Domino and Line Sudoku. In October 2020, a Kickstarter crowdfunding campaign was announced in order to produce a physical book with some of the channel's most popular puzzles.
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