001 /*
002 * Created on Sep 21, 2004
003 *
004 */
005 package aima.search.csp;
006
007 import java.util.ArrayList;
008 import java.util.Hashtable;
009 import java.util.Iterator;
010 import java.util.List;
011
012 /**
013 * @author Ravi Mohan
014 *
015 */
016
017 public class Assignment {
018 Hashtable<String, Object> variablesToValues;
019
020 List<String> variables;
021
022 public Assignment() {
023 this(new ArrayList<String>());
024 }
025
026 public Assignment(List<String> variables) {
027 variablesToValues = new Hashtable<String, Object>();
028 this.variables = variables;
029 }
030
031 public void setAssignment(String variable, Object value) {
032 variablesToValues.put(variable, value);
033 }
034
035 public Object getAssignment(String variable) {
036 return variablesToValues.get(variable);
037 }
038
039 public boolean isComplete() {
040
041 return everyVariableIsAKeyAndHasAValue();
042 }
043
044 private boolean everyVariableIsAKeyAndHasAValue() {
045
046 Iterator iter = variables.iterator();
047 while (iter.hasNext()) {
048 String variable = (String) iter.next();
049 if (!variablesToValues.keySet().contains(variable)) {
050 return false;
051 } else {
052 if (variablesToValues.get(variable) == null) {
053 return false;
054 }
055 }
056 }
057 return true;
058 }
059
060 public void remove(String variable) {
061 if (variablesToValues.keySet().contains(variable)) {
062 variablesToValues.remove(variable);
063 }
064 }
065
066 public String selectFirstUnassignedVariable() {
067 Iterator iter = variables.iterator();
068 while (iter.hasNext()) {
069 String variable = (String) iter.next();
070 if (!(variablesToValues.keySet().contains(variable))) {
071 return variable;
072 }
073 }
074 return null;
075
076 }
077
078 public boolean hasAssignmentFor(String variable) {
079 return variablesToValues.keySet().contains(variable);
080 }
081
082 @Override
083 public String toString() {
084
085 return variablesToValues.toString();
086 }
087
088 public Assignment copy() {
089 Assignment copy = new Assignment();
090 for (int i = 0; i < variables.size(); i++) {
091 copy.variables.add(variables.get(i));
092 }
093 Iterator<String> iter = variablesToValues.keySet().iterator();
094 while (iter.hasNext()) {
095 String key = iter.next();
096 copy.variablesToValues.put(key, variablesToValues.get(key));
097 }
098 return copy;
099 }
100
101 public int getNumberOfConflictsFor(String conflictedVariable, Object value,
102 Constraint constraint) {
103 Assignment duplicate = copy();
104 duplicate.setAssignment(conflictedVariable, value);
105 return duplicate.getConflictedVariables(constraint).size();
106 }
107
108 public List<String> getConflictedVariables(Constraint constraint) {
109 List<String> conflictedVariables = new ArrayList<String>();
110 List<String> variables = getVariables();
111 for (String variable : variables) {
112 Object value = getAssignment(variable);
113 if (!(constraint.isSatisfiedWith(this, variable, value))) {
114 conflictedVariables.add(variable);
115 }
116 }
117 return conflictedVariables;
118 }
119
120 public Object getMinimumConflictingValueFor(String conflictedVariable,
121 List domain, Constraint constraint) {
122 int minConflict = Integer.MAX_VALUE;
123 Object minConflictValue = null;
124
125 for (int i = 0; i < domain.size(); i++) {
126 Object value = domain.get(i);
127 if (getNumberOfConflictsFor(conflictedVariable, value, constraint) < minConflict) {
128 minConflict = getNumberOfConflictsFor(conflictedVariable,
129 value, constraint);
130 minConflictValue = value;
131 }
132 }
133 return minConflictValue;
134 }
135
136 public boolean satisfies(Constraint constraint) {
137 if (isComplete()) {
138 for (int j = 0; j < getVariables().size(); j++) {
139 String variable = getVariables().get(j);
140 Object value = getAssignment(variable);
141 if (!(constraint.isSatisfiedWith(this, variable, value))) {
142 return false;
143 }
144 }
145 return true;
146 } else {
147 return false;
148 }
149 }
150
151 public List<String> getVariables() {
152 return variables;
153 }
154 }