8927b03942
Some of these imports are not used. The rest of them only import string to use the string.atoi function. But string.atoi(s) on a string input is identical to just int(s). See the docs: "deprecated since 2.0".
115 lines
3.1 KiB
Python
115 lines
3.1 KiB
Python
# Copyright 2010 Hakan Kjellerstrand hakank@bonetmail.com
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""
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Langford's number problem in Google CP Solver.
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Langford's number problem (CSP lib problem 24)
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http://www.csplib.org/prob/prob024/
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'''
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Arrange 2 sets of positive integers 1..k to a sequence,
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such that, following the first occurence of an integer i,
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each subsequent occurrence of i, appears i+1 indices later
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than the last.
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For example, for k=4, a solution would be 41312432
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'''
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* John E. Miller: Langford's Problem
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http://www.lclark.edu/~miller/langford.html
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* Encyclopedia of Integer Sequences for the number of solutions for each k
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http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=014552
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Also, see the following models:
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* MiniZinc: http://www.hakank.org/minizinc/langford2.mzn
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* Gecode/R: http://www.hakank.org/gecode_r/langford.rb
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* ECLiPSe: http://hakank.org/eclipse/langford.ecl
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* SICStus: http://hakank.org/sicstus/langford.pl
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This model was created by Hakan Kjellerstrand (hakank@bonetmail.com)
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Also see my other Google CP Solver models:
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http://www.hakank.org/google_or_tools/
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"""
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import sys
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from ortools.constraint_solver import pywrapcp
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def main(k=8, num_sol=0):
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# Create the solver.
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solver = pywrapcp.Solver("Langford")
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#
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# data
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#
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print "k:", k
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p = range(2 * k)
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#
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# declare variables
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#
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position = [solver.IntVar(0, 2 * k - 1, "position[%i]" % i) for i in p]
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solution = [solver.IntVar(1, k, "position[%i]" % i) for i in p]
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#
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# constraints
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#
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solver.Add(solver.AllDifferent(position))
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for i in range(1, k + 1):
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solver.Add(position[i + k - 1] == position[i - 1] + i + 1)
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solver.Add(solver.Element(solution, position[i - 1]) == i)
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solver.Add(solver.Element(solution, position[k + i - 1]) == i)
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# symmetry breaking
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solver.Add(solution[0] < solution[2 * k - 1])
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#
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# search and result
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#
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db = solver.Phase(position,
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solver.CHOOSE_FIRST_UNBOUND,
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solver.ASSIGN_MIN_VALUE)
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solver.NewSearch(db)
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num_solutions = 0
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while solver.NextSolution():
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print "solution:", ",".join([str(solution[i].Value()) for i in p])
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num_solutions += 1
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if num_sol > 0 and num_solutions >= num_sol:
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break
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solver.EndSearch()
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print
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print "num_solutions:", num_solutions
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print "failures:", solver.Failures()
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print "branches:", solver.Branches()
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print "WallTime:", solver.WallTime()
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k = 8
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num_sol = 0
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if __name__ == "__main__":
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if len(sys.argv) > 1:
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k = int(sys.argv[1])
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if len(sys.argv) > 2:
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num_sol = int(sys.argv[2])
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main(k, num_sol)
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