548.exchange2_r
Michael Metcalf, Berlin
Michael Metcalf is the author of many articles and books on Fortran.
Games: Sudoku Puzzle Generator
This program was written for development of non-trivial 9x9 sudoku puzzles. It has been used extensively in informal competitions, which run for days. Incidentally, it tests many Fortran 95 array handling features (including some intrinsic functions) for use with integer arrays. Unusually, it relies heavily on recursion (up to eight levels deep) but, in contrast to most Fortran programs, uses no floating-point arithmetic.
The input data file contains in each record a valid sudoku puzzle (one that has one and only one solution). It is represented as a string of 81 digits, 1 to 9 for the clues, and 0 for the empty cells. Each puzzle acts as a seed for the production of further valid puzzles with an identical pattern of clues. For convenience, the submitted program contains a data set of 27 puzzles in the form of an initialization expression. A second set can be extracted from the first by not transposing the puzzle on input.
The file s.txt contains each new puzzle as an 81-digit string followed by a sequence number and 1 or 2 codes.
Fortran 95
None
Exchange2 is licensed directly to SPEC by the author, Michael Metcalf.
Last updated: $Date: 2020-08-19 18:52:31 -0400 (Wed, 19 Aug 2020) $
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