001 package aima.search.csp;
002
003 import java.util.ArrayList;
004 import java.util.List;
005
006 import aima.util.Util;
007
008 /**
009 * @author Ravi Mohan
010 *
011 */
012
013 public class CSP {
014
015 // private Assignment assignment;
016
017 private Domain domains;
018
019 private Constraint constraints;
020
021 private List<String> variables;
022
023 public CSP(List<String> variables, Constraint constraints) {
024 this.variables = variables;
025 // this.assignment = new Assignment(variables);
026 this.domains = new Domain(variables);
027 this.constraints = constraints;
028 }
029
030 public CSP(List<String> variables, Constraint constraints, Domain domains) {
031 this.variables = variables;
032 // this.assignment = new Assignment(variables);
033 this.domains = domains;
034 this.constraints = constraints;
035 }
036
037 public List defaultOrderDomainOf(String variable) {
038 return domains.getDomainOf(variable);
039 }
040
041 public Assignment backTrackingSearch() {
042 return recursiveBackTrackingSearch(new Assignment(variables));
043 }
044
045 private Assignment recursiveBackTrackingSearch(Assignment anAssignment) {
046 if (anAssignment.isComplete()) {
047 return anAssignment;
048 }
049 String variable = anAssignment.selectFirstUnassignedVariable();
050 List domainValues = defaultOrderDomainOf(variable);
051 for (int i = 0; i < domainValues.size(); i++) {
052 Object value = domainValues.get(i);
053
054 if (constraints.isSatisfiedWith(anAssignment, variable, value)) {
055 anAssignment.setAssignment(variable, value);
056 Assignment result = recursiveBackTrackingSearch(anAssignment);
057 if (result != null) {
058 return result;
059 }
060 anAssignment.remove(variable);
061 }
062 }
063 return null;// failure
064 }
065
066 public Assignment mcSearch(int maxSteps) {
067 Assignment randomAssignment = generateRandomAssignment();
068
069 for (int i = 0; i < maxSteps; i++) {
070
071 if (randomAssignment.satisfies(constraints)) {
072 return randomAssignment;
073 } else {
074 String conflictedVariable = Util
075 .selectRandomlyFromList(randomAssignment
076 .getConflictedVariables(constraints));
077 Object minConflictValue = randomAssignment
078 .getMinimumConflictingValueFor(conflictedVariable,
079 domains.getDomainOf(conflictedVariable),
080 constraints);
081 randomAssignment.setAssignment(conflictedVariable,
082 minConflictValue);
083 }
084 }
085 return null;
086
087 }
088
089 private Assignment generateRandomAssignment() {
090 List<String> vars = new ArrayList<String>();
091 for (int i = 0; i < variables.size(); i++) {
092 vars.add(variables.get(i));
093 }
094 Assignment assignment = new Assignment(vars);
095 for (int i = 0; i < variables.size(); i++) {
096 String variable = variables.get(i);
097 Object randomValue = Util.selectRandomlyFromList(domains
098 .getDomainOf(variable));
099 // System.out.println("in generate Assignment setting");
100 assignment.setAssignment(variable, randomValue);
101 }
102 return assignment;
103 }
104
105 }