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".
139 lines
3.8 KiB
Python
139 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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Traffic lights problem in Google CP Solver.
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CSPLib problem 16
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http://www.cs.st-andrews.ac.uk/~ianm/CSPLib/prob/prob016/index.html
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'''
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Specification:
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Consider a four way traffic junction with eight traffic lights. Four of the
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traffic
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lights are for the vehicles and can be represented by the variables V1 to V4
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with domains
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{r,ry,g,y} (for red, red-yellow, green and yellow). The other four traffic
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lights are
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for the pedestrians and can be represented by the variables P1 to P4 with
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domains {r,g}.
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The constraints on these variables can be modelled by quaternary constraints
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on
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(Vi, Pi, Vj, Pj ) for 1<=i<=4, j=(1+i)mod 4 which allow just the tuples
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{(r,r,g,g), (ry,r,y,r), (g,g,r,r), (y,r,ry,r)}.
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It would be interesting to consider other types of junction (e.g. five roads
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intersecting) as well as modelling the evolution over time of the traffic
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light sequence.
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...
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Results
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Only 2^2 out of the 2^12 possible assignments are solutions.
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(V1,P1,V2,P2,V3,P3,V4,P4) =
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{(r,r,g,g,r,r,g,g), (ry,r,y,r,ry,r,y,r), (g,g,r,r,g,g,r,r),
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(y,r,ry,r,y,r,ry,r)}
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[(1,1,3,3,1,1,3,3), ( 2,1,4,1, 2,1,4,1), (3,3,1,1,3,3,1,1), (4,1, 2,1,4,1,
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2,1)}
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The problem has relative few constraints, but each is very tight. Local
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propagation
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appears to be rather ineffective on this problem.
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'''
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Note: In this model we use only the constraint solver.AllowedAssignments().
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Compare with these models:
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* MiniZinc: http://www.hakank.org/minizinc/traffic_lights.mzn
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* Comet : http://www.hakank.org/comet/traffic_lights.co
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* ECLiPSe : http://www.hakank.org/eclipse/traffic_lights.ecl
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* Gecode : http://hakank.org/gecode/traffic_lights.cpp
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* SICStus : http://hakank.org/sicstus/traffic_lights.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(base=10, start=1, len1=1, len2=4):
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# Create the solver.
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solver = pywrapcp.Solver("Traffic lights")
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#
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# data
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#
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n = 4
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r, ry, g, y = range(n)
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lights = ["r", "ry", "g", "y"]
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# The allowed combinations
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allowed = []
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allowed.extend([(r, r, g, g),
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(ry, r, y, r),
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(g, g, r, r),
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(y, r, ry, r)])
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#
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# declare variables
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#
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V = [solver.IntVar(0, n - 1, "V[%i]" % i) for i in range(n)]
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P = [solver.IntVar(0, n - 1, "P[%i]" % i) for i in range(n)]
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#
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# constraints
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#
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for i in range(n):
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for j in range(n):
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if j == (1 + i) % n:
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solver.Add(solver.AllowedAssignments((V[i], P[i], V[j], P[j]), allowed))
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#
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# Search and result
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#
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db = solver.Phase(V + P,
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solver.INT_VAR_SIMPLE,
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solver.INT_VALUE_DEFAULT)
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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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for i in range(n):
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print "%+2s %+2s" % (lights[V[i].Value()], lights[P[i].Value()]),
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print
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num_solutions += 1
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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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print
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if __name__ == "__main__":
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main()
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