139 lines
4.3 KiB
C#
139 lines
4.3 KiB
C#
//
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// Copyright 2012 Hakan Kjellerstrand
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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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using System;
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using System.Collections;
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using System.IO;
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using System.Text.RegularExpressions;
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using Google.OrTools.ConstraintSolver;
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public class TrafficLights
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{
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/**
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*
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* Traffic lights problem.
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*
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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 lights are for the vehicles and can be represented by the variables
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* V1 to V4 with domains {r,ry,g,y} (for red, red-yellow, green and yellow).
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* The other four traffic lights are for the pedestrians and can be
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* represented by the variables P1 to P4 with domains {r,g}.
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*
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* The constraints on these variables can be modelled by quaternary
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* constraints on (Vi, Pi, Vj, Pj ) for 1<=i<=4, j=(1+i)mod 4 which allow just
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* 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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*
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* It would be interesting to consider other types of junction (e.g. five
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* roads intersecting) as well as modelling the evolution over time of the
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* traffic light sequence.
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* ...
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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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*
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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)} The problem has relative few constraints, but each is very tight.
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* Local propagation appears to be rather ineffective on this problem.
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*
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* """
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* Note: In this model we use only the constraint
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* solver.AllowedAssignments().
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*
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*
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* See http://www.hakank.org/or-tools/traffic_lights.py
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*
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*/
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private static void Solve()
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{
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Solver solver = new Solver("TrafficLights");
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//
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// data
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//
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int n = 4;
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int r = 0;
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int ry = 1;
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int g = 2;
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int y = 3;
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string[] lights = { "r", "ry", "g", "y" };
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// The allowed combinations
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IntTupleSet allowed = new IntTupleSet(4);
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allowed.InsertAll(new long[][] { new long[] { r, r, g, g }, new long[] { ry, r, y, r },
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new long[] { g, g, r, r }, new long[] { y, r, ry, r } });
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//
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// Decision variables
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//
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IntVar[] V = solver.MakeIntVarArray(n, 0, n - 1, "V");
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IntVar[] P = solver.MakeIntVarArray(n, 0, n - 1, "P");
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// for search
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IntVar[] VP = new IntVar[2 * n];
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for (int i = 0; i < n; i++)
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{
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VP[i] = V[i];
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VP[i + n] = P[i];
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}
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//
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// Constraints
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//
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for (int i = 0; i < n; i++)
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{
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int j = (1 + i) % n;
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IntVar[] tmp = new IntVar[] { V[i], P[i], V[j], P[j] };
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solver.Add(tmp.AllowedAssignments(allowed));
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}
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//
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// Search
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//
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DecisionBuilder db = solver.MakePhase(VP, Solver.CHOOSE_FIRST_UNBOUND, Solver.ASSIGN_MIN_VALUE);
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solver.NewSearch(db);
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while (solver.NextSolution())
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{
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for (int i = 0; i < n; i++)
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{
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Console.Write("{0,2} {1,2} ", lights[V[i].Value()], lights[P[i].Value()]);
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}
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Console.WriteLine();
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}
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Console.WriteLine("\nSolutions: {0}", solver.Solutions());
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Console.WriteLine("WallTime: {0}ms", solver.WallTime());
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Console.WriteLine("Failures: {0}", solver.Failures());
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Console.WriteLine("Branches: {0} ", solver.Branches());
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solver.EndSearch();
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}
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public static void Main(String[] args)
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{
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Solve();
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}
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}
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