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A330280
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Least number of 2 X 2 rotations required to solve an n X n Simon Tatham's Twiddle puzzle.
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1
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OFFSET
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1,2
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COMMENTS
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The puzzle is as follows. An n X n grid is filled with distinct integers from 1 to n*n, such that the number at row r and column c (both 0-based) is n*n - (r*n + c). The task is to perform rotations of 2 X 2 sub-grids (moves) to bring the numbers into their natural order, i.e., the number at row r and column c should become r*n + c + 1. Rotations are by 90 degrees in the clockwise or counterclockwise direction. See links for example puzzles and solutions.
Wladimir Leite found strong upper bounds for the next few terms: 48, 88 and 146 (see links). - Dmitry Kamenetsky, Apr 20 2020
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LINKS
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CROSSREFS
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KEYWORD
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nonn,hard,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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