Abstract

The Sudoku problem is a well-known logic-based puzzle of combinatorial number-placement. It consists in filling a n 2 × n 2 grid, composed of n columns, n rows, and n subgrids, each one containing distinct integers from 1 to n 2. Such a puzzle belongs to the NP-complete collection of problems, to which there exist diverse exact and approximate methods able to solve it. In this paper, we propose a new hybrid algorithm that smartly combines a classic tabu search procedure with the alldifferent global constraint from the constraint programming world. The alldifferent constraint is known to be efficient for domain filtering in the presence of constraints that must be pairwise different, which are exactly the kind of constraints that Sudokus own. This ability clearly alleviates the work of the tabu search, resulting in a faster and more robust approach for solving Sudokus. We illustrate interesting experimental results where our proposed algorithm outperforms the best results previously reported by hybrids and approximate methods.

Highlights

  • The Sudoku puzzle is a combinatorial problem consisting of assigning n2 digits, from 1 to n2, in each cell matrix of size n2 × n2

  • The tested benchmarks are classified in diverse kinds of complexity, including the AI Escargot which is considered the most difficult instance [28]

  • We have presented a new hybrid that integrates the powerful alldifferent constraint into a classic tabu search algorithm

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Summary

A Hybrid alldifferent-Tabu Search Algorithm for Solving Sudoku Puzzles

The Sudoku problem is a well-known logic-based puzzle of combinatorial number-placement It consists in filling a n2 × n2 grid, composed of n columns, n rows, and n subgrids, each one containing distinct integers from 1 to n2. Such a puzzle belongs to the NPcomplete collection of problems, to which there exist diverse exact and approximate methods able to solve it. The alldifferent constraint is known to be efficient for domain filtering in the presence of constraints that must be pairwise different, which are exactly the kind of constraints that Sudokus own This ability clearly alleviates the work of the tabu search, resulting in a faster and more robust approach for solving Sudokus. We illustrate interesting experimental results where our proposed algorithm outperforms the best results previously reported by hybrids and approximate methods

Introduction
Related Work
Tabu Search
CP Overview and the alldifferent Constraint
Proposed Algorithm
Experimental Results
Conclusion and Future Work
E Easy 3 4 5 C D Medium Hard SD AI Escargot

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