Mercurial > repos > shellac > sam_consensus_v3
diff env/lib/python3.9/site-packages/networkx/generators/sudoku.py @ 0:4f3585e2f14b draft default tip
"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
author | shellac |
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date | Mon, 22 Mar 2021 18:12:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/env/lib/python3.9/site-packages/networkx/generators/sudoku.py Mon Mar 22 18:12:50 2021 +0000 @@ -0,0 +1,128 @@ +"""Generator for Sudoku graphs + +This module gives a generator for n-Sudoku graphs. It can be used to develop +algorithms for solving or generating Sudoku puzzles. + +A completed Sudoku grid is a 9x9 array of integers between 1 and 9, with no +number appearing twice in the same row, column, or 3x3 box. + + 8 6 4 | 3 7 1 | 2 5 9 + 3 2 5 | 8 4 9 | 7 6 1 + 9 7 1 | 2 6 5 | 8 4 3 + ------+-------+------ + 4 3 6 | 1 9 2 | 5 8 7 + 1 9 8 | 6 5 7 | 4 3 2 + 2 5 7 | 4 8 3 | 9 1 6 + ------+-------+------ + 6 8 9 | 7 3 4 | 1 2 5 + 7 1 3 | 5 2 8 | 6 9 4 + 5 4 2 | 9 1 6 | 3 7 8 + + +The Sudoku graph is an undirected graph with 81 vertices, corresponding to +the cells of a Sudoku grid. It is a regular graph of degree 20. Two distinct +vertices are adjacent if and only if the corresponding cells belong to the +same row, column, or box. A completed Sudoku grid corresponds to a vertex +coloring of the Sudoku graph with nine colors. + +More generally, the n-Sudoku graph is a graph with n^4 vertices, corresponding +to the cells of an n^2 by n^2 grid. Two distinct vertices are adjacent if and +only if they belong to the same row, column, or n by n box. + +References +---------- +.. [1] Herzberg, A. M., & Murty, M. R. (2007). Sudoku squares and chromatic + polynomials. Notices of the AMS, 54(6), 708-717. +.. [2] Sander, Torsten (2009), "Sudoku graphs are integral", + Electronic Journal of Combinatorics, 16 (1): Note 25, 7pp, MR 2529816 +.. [3] Wikipedia contributors. "Glossary of Sudoku." Wikipedia, The Free + Encyclopedia, 3 Dec. 2019. Web. 22 Dec. 2019. +""" + +import networkx as nx +from networkx.exception import NetworkXError + +__all__ = ["sudoku_graph"] + + +def sudoku_graph(n=3): + """Returns the n-Sudoku graph. The default value of n is 3. + + The n-Sudoku graph is a graph with n^4 vertices, corresponding to the + cells of an n^2 by n^2 grid. Two distinct vertices are adjacent if and + only if they belong to the same row, column, or n-by-n box. + + Parameters + ---------- + n: integer + The order of the Sudoku graph, equal to the square root of the + number of rows. The default is 3. + + Returns + ------- + NetworkX graph + The n-Sudoku graph Sud(n). + + Examples + -------- + >>> G = nx.sudoku_graph() + >>> G.number_of_nodes() + 81 + >>> G.number_of_edges() + 810 + >>> sorted(G.neighbors(42)) + [6, 15, 24, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 51, 52, 53, 60, 69, 78] + >>> G = nx.sudoku_graph(2) + >>> G.number_of_nodes() + 16 + >>> G.number_of_edges() + 56 + + References + ---------- + .. [1] Herzberg, A. M., & Murty, M. R. (2007). Sudoku squares and chromatic + polynomials. Notices of the AMS, 54(6), 708-717. + .. [2] Sander, Torsten (2009), "Sudoku graphs are integral", + Electronic Journal of Combinatorics, 16 (1): Note 25, 7pp, MR 2529816 + .. [3] Wikipedia contributors. "Glossary of Sudoku." Wikipedia, The Free + Encyclopedia, 3 Dec. 2019. Web. 22 Dec. 2019. + """ + + if n < 0: + raise NetworkXError("The order must be greater than or equal to zero.") + + n2 = n * n + n3 = n2 * n + n4 = n3 * n + + # Construct an empty graph with n^4 nodes + G = nx.empty_graph(n4) + + # A Sudoku graph of order 0 or 1 has no edges + if n < 2: + return G + + # Add edges for cells in the same row + for row_no in range(0, n2): + row_start = row_no * n2 + for j in range(1, n2): + for i in range(j): + G.add_edge(row_start + i, row_start + j) + + # Add edges for cells in the same column + for col_no in range(0, n2): + for j in range(col_no, n4, n2): + for i in range(col_no, j, n2): + G.add_edge(i, j) + + # Add edges for cells in the same box + for band_no in range(n): + for stack_no in range(n): + box_start = n3 * band_no + n * stack_no + for j in range(1, n2): + for i in range(j): + u = box_start + (i % n) + n2 * (i // n) + v = box_start + (j % n) + n2 * (j // n) + G.add_edge(u, v) + + return G