2. The Test Cell Algorithm
The Test Cell algorithm developed for solving Sudoku puzzles does not mimic human logic or hand-developed algorithms. It is a straightforward, easy to implement, consistent and efficient computer-based algorithm that employs Test Cells - special testing cells determined by a specific criterion, that guide to the ultimate puzzle solution. While absent in typical easy puzzles (as a solution is reached without a need to identify them), Test Cells begin to appear as the difficulty of the puzzle is raised. Though only tested on 9X9 Sudoku grids, the Test Cell algorithm can ideally be scaled to other puzzle dimensions.
Introduced in Japan in 1984 and made world popular by British newspaper London Times in 2005-, the Sudoku puzzle has become the passion of many people the world over in the past few years. Sudoku is a logic-based, combinatorial number-placement puzzle whose objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid (also called "boxes", "blocks", "regions", or "sub-squares") contains all of the digits from 1 to 9. The puzzle is a partially completed grid and does not necessarily have a single legitimate solution. Ironically, despite being a game of numbers, Sudoku doesn‟t demand an iota of mathematics of its solvers. In fact, no operation—including addition or multiplication helps in completing a grid, which in theory could be filled with any set of nine different symbols. Nevertheless, Sudoku presents mathematicians and computer scientists a host of challenging issues viz. the choice of the number of Sudoku grids that can be constructed, the minimal number of starting clues that yield a unique solution, and, whether Sudoku belongs to the N-P complete class of problems. Unlike manually solving the puzzle with hand-developed algorithms or natural methods, computer-based algorithms offer quick solutions to Sudoku puzzles, even with rigorous backtracking - a systematic form of trial and error in which partial solutions are proposed and slightly modified if proved wrong. Challenging puzzles however
The Test Cell algorithm is better explained by a preliminary description of all terms pertaining to it in an intended logical order. These are: Lists- An empty cell has a set of numbers that cannot occupy it (Impossibility List) and consequently, a corresponding set of those that can occupy it (Possibility List). These lists are developed for every empty cell according to the Sudoku game rules. Invalid Puzzle Configuration- A puzzle configuration in which there is...