//
// Copyright 2012 Hakan Kjellerstrand
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
using System;
using System.Collections;
using System.IO;
using System.Text.RegularExpressions;
using Google.OrTools.ConstraintSolver;
public class TrafficLights
{
/**
*
* Traffic lights problem.
*
* CSPLib problem 16
* http://www.cs.st-andrews.ac.uk/~ianm/CSPLib/prob/prob016/index.html
* """
* Specification:
* Consider a four way traffic junction with eight traffic lights. Four of the traffic
* lights are for the vehicles and can be represented by the variables V1 to V4 with domains
* {r,ry,g,y} (for red, red-yellow, green and yellow). The other four traffic lights are
* for the pedestrians and can be represented by the variables P1 to P4 with domains {r,g}.
*
* The constraints on these variables can be modelled by quaternary constraints on
* (Vi, Pi, Vj, Pj ) for 1<=i<=4, j=(1+i)mod 4 which allow just the tuples
* {(r,r,g,g), (ry,r,y,r), (g,g,r,r), (y,r,ry,r)}.
*
* It would be interesting to consider other types of junction (e.g. five roads
* intersecting) as well as modelling the evolution over time of the traffic light sequence.
* ...
*
* Results
* Only 2^2 out of the 2^12 possible assignments are solutions.
*
* (V1,P1,V2,P2,V3,P3,V4,P4) =
* {(r,r,g,g,r,r,g,g), (ry,r,y,r,ry,r,y,r), (g,g,r,r,g,g,r,r), (y,r,ry,r,y,r,ry,r)}
* [(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, 2,1)}
* The problem has relative few constraints, but each is very
* tight. Local propagation appears to be rather ineffective on this
* problem.
*
* """
* Note: In this model we use only the constraint
* solver.AllowedAssignments().
*
*
* See http://www.hakank.org/or-tools/traffic_lights.py
*
*/
private static void Solve()
{
Solver solver = new Solver("TrafficLights");
//
// data
//
int n = 4;
int r = 0;
int ry = 1;
int g = 2;
int y = 3;
string[] lights = {"r", "ry", "g", "y"};
// The allowed combinations
IntTupleSet allowed = new IntTupleSet(4);
allowed.InsertAll(new int[,] {{r,r,g,g},
{ry,r,y,r},
{g,g,r,r},
{y,r,ry,r}});
//
// Decision variables
//
IntVar[] V = solver.MakeIntVarArray(n, 0, n-1, "V");
IntVar[] P = solver.MakeIntVarArray(n, 0, n-1, "P");
// for search
IntVar[] VP = new IntVar[2 * n];
for(int i = 0; i < n; i++) {
VP[i] = V[i];
VP[i+n] = P[i];
}
//
// Constraints
//
for(int i = 0; i < n; i++) {
int j = (1+i) % n;
IntVar[] tmp = new IntVar[] {V[i],P[i],V[j],P[j]};
solver.Add(tmp.AllowedAssignments(allowed));
}
//
// Search
//
DecisionBuilder db = solver.MakePhase(VP,
Solver.CHOOSE_FIRST_UNBOUND,
Solver.ASSIGN_MIN_VALUE);
solver.NewSearch(db);
while (solver.NextSolution()) {
for(int i = 0; i < n; i++) {
Console.Write("{0,2} {1,2} ",
lights[V[i].Value()],
lights[P[i].Value()]);
}
Console.WriteLine();
}
Console.WriteLine("\nSolutions: {0}", solver.Solutions());
Console.WriteLine("WallTime: {0}ms", solver.WallTime());
Console.WriteLine("Failures: {0}", solver.Failures());
Console.WriteLine("Branches: {0} ", solver.Branches());
solver.EndSearch();
}
public static void Main(String[] args)
{
Solve();
}
}