118 lines
3.8 KiB
Python
118 lines
3.8 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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Secret Santa problem in Google CP Solver.
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From Ruby Quiz Secret Santa
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http://www.rubyquiz.com/quiz2.html
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'''
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Honoring a long standing tradition started by my wife's dad, my friends
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all play a Secret Santa game around Christmas time. We draw names and
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spend a week sneaking that person gifts and clues to our identity. On the
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last night of the game, we get together, have dinner, share stories, and,
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most importantly, try to guess who our Secret Santa was. It's a crazily
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fun way to enjoy each other's company during the holidays.
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To choose Santas, we use to draw names out of a hat. This system was
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tedious, prone to many 'Wait, I got myself...' problems. This year, we
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made a change to the rules that further complicated picking and we knew
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the hat draw would not stand up to the challenge. Naturally, to solve
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this problem, I scripted the process. Since that turned out to be more
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interesting than I had expected, I decided to share.
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This weeks Ruby Quiz is to implement a Secret Santa selection script.
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Your script will be fed a list of names on STDIN.
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...
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Your script should then choose a Secret Santa for every name in the list.
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Obviously, a person cannot be their own Secret Santa. In addition, my friends
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no longer allow people in the same family to be Santas for each other and your
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script should take this into account.
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'''
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Comment: This model skips the file input and mail parts. We
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assume that the friends are identified with a number from 1..n,
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and the families is identified with a number 1..num_families.
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Compare with the following model:
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* MiniZinc: http://www.hakank.org/minizinc/secret_santa.mzn
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This model gives 4089600 solutions and the following statistics:
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- failures: 31264
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- branches: 8241726
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- wall_time: 23735 ms (note: without any printing of the solutions)
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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: http://www.hakank.org/google_or_tools/
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"""
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import sys
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from constraint_solver import pywrapcp
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def main():
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# Create the solver.
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solver = pywrapcp.Solver('Secret Santa problem')
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#
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# data
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#
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family = [1,1,1,1, 2, 3,3,3,3,3, 4,4]
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num_families = max(family)
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n = len(family)
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#
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# declare variables
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#
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x = [solver.IntVar(0, n-1, 'x[%i]' % i) for i in range(n)]
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#
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# constraints
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#
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solver.Add(solver.AllDifferent(x, True))
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# Can't be one own's Secret Santa
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# Ensure that there are no fix-point in the array
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for i in range(n):
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solver.Add(x[i] != i)
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# No Secret Santa to a person in the same family
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for i in range(n):
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solver.Add(family[i] != solver.Element(family, x[i]))
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#
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# solution and search
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#
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db = solver.Phase(x,
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solver.INT_VAR_SIMPLE,
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solver.INT_VALUE_SIMPLE)
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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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num_solutions += 1
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print 'x:', [x[i].Value() for i in range(n)]
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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 'wall_time:', solver.wall_time(), 'ms'
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if __name__ == '__main__':
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main()
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