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The classic textbook example of the use of backtracking is the eight queens puzzle, that asks for all arrangements of eight chess queens on a standard chessboard so that no queen attacks any other. In the common backtracking approach, the partial candidates are arrangements of k queens in the first k rows of the board, all in different rows and ...
One way to speed up a brute-force algorithm is to reduce the search space, that is, the set of candidate solutions, by using heuristics specific to the problem class. For example, in the eight queens problem the challenge is to place eight queens on a standard chessboard so that no queen attacks any other.
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The GNU Prolog program below resolved a 100 queens problem in less than a tenth of a second. is meaningless without a frame of reference. Giving at least the processor used for the test and the time of a slower algorithm would help matters greatly. Andrew J. MacDonald 03:51, 30 November 2006 (UTC)
Nauck also extended the puzzle to the n queens problem, with n queens on a chessboard of n×n squares. Since then, many mathematicians, including Carl Friedrich Gauss, have worked on both the eight queens puzzle and its generalized n-queens version. In 1874, S. Günther proposed a method using determinants to find solutions. [1]
B-Prolog is a commercial product, but it can be used for learning and non-profit research purposes free of charge (since version 7.8 for individual users, including commercial individual users, B-Prolog is free of charge [4]). B-Prolog is not anymore actively developed, but it forms the basis for the Picat programming language.
This generates sentences such as "the cat eats the bat", "a bat eats the cat". One can generate all of the valid expressions in the language generated by this grammar at a Prolog interpreter by typing sentence(X,[]). Similarly, one can test whether a sentence is valid in the language by typing something like sentence([the,bat,eats,the,bat],[]).
The program complexity is the complexity of the decision problem when A and R are inputs and E is fixed. The combined complexity is the complexity of the decision problem when A, E, and R are inputs. With respect to data complexity, the decision problem for Datalog is P-complete (See Theorem 4.4 in [25]). P-completeness for data complexity ...