Proofed chapter 3

CCSPiJ/src/chapter3/CSP.java

@@ -24,12 +24,11 @@
 public class CSP<V, D> {
 	private List<V> variables;
 	private Map<V, List<D>> domains;
-	private Map<V, List<Constraint<V, D>>> constraints;
+	private Map<V, List<Constraint<V, D>>> constraints = new HashMap<>();
 
 	public CSP(List<V> variables, Map<V, List<D>> domains) {
 		this.variables = variables;
 		this.domains = domains;
-		constraints = new HashMap<>();
 		for (V variable : variables) {
 			constraints.put(variable, new ArrayList<>());
 			if (!domains.containsKey(variable)) {
@@ -42,9 +41,8 @@ public void addConstraint(Constraint<V, D> constraint) {
 		for (V variable : constraint.variables) {
 			if (!variables.contains(variable)) {
 				throw new IllegalArgumentException("Variable in constraint not in CSP");
-			} else {
-				constraints.get(variable).add(constraint);
 			}
+			constraints.get(variable).add(constraint);
 		}
 	}
 
@@ -65,7 +63,7 @@ public Map<V, D> backtrackingSearch(Map<V, D> assignment) {
 			return assignment;
 		}
 		// get the first variable in the CSP but not in the assignment
-		V unassigned = variables.stream().filter(v -> (!assignment.containsKey(v))).findFirst().get();
+		V unassigned = variables.stream().filter(v -> !assignment.containsKey(v)).findFirst().get();
 		// get the every possible domain value of the first unassigned variable
 		for (D value : domains.get(unassigned)) {
 			// shallow copy of assignment that we can change

CCSPiJ/src/chapter3/MapColoringConstraint.java

@@ -21,6 +21,15 @@
 import java.util.Map;
 
 public final class MapColoringConstraint extends Constraint<String, String> {
+
+	private static final String WESTERN = "Western Australia";
+	private static final String NORTHERN = "Northern Territory";
+	private static final String SOUTH = "South Australia";
+	private static final String QUEENSLAND = "Queensland";
+	private static final String NEW_SOUTH_WALES = "New South Wales";
+	private static final String VICTORIA = "Victoria";
+	private static final String TASMANIA =  "Tasmania";
+
 	private String place1, place2;
 
 	public MapColoringConstraint(String place1, String place2) {
@@ -42,23 +51,23 @@ public boolean satisfied(Map<String, String> assignment) {
 	}
 
 	public static void main(String[] args) {
-		List<String> variables = List.of("Western Australia", "Northern Territory",
-				"South Australia", "Queensland", "New South Wales", "Victoria", "Tasmania");
+		List<String> variables = List.of(WESTERN, NORTHERN, SOUTH, QUEENSLAND,
+				NEW_SOUTH_WALES, VICTORIA, TASMANIA);
 		Map<String, List<String>> domains = new HashMap<>();
 		for (String variable : variables) {
 			domains.put(variable, List.of("red", "green", "blue"));
 		}
 		CSP<String, String> csp = new CSP<>(variables, domains);
-		csp.addConstraint(new MapColoringConstraint("Western Australia", "Northern Territory"));
-		csp.addConstraint(new MapColoringConstraint("Western Australia", "South Australia"));
-		csp.addConstraint(new MapColoringConstraint("South Australia", "Northern Territory"));
-		csp.addConstraint(new MapColoringConstraint("Queensland", "Northern Territory"));
-		csp.addConstraint(new MapColoringConstraint("Queensland", "South Australia"));
-		csp.addConstraint(new MapColoringConstraint("Queensland", "New South Wales"));
-		csp.addConstraint(new MapColoringConstraint("New South Wales", "South Australia"));
-		csp.addConstraint(new MapColoringConstraint("Victoria", "South Australia"));
-		csp.addConstraint(new MapColoringConstraint("Victoria", "New South Wales"));
-		csp.addConstraint(new MapColoringConstraint("Victoria", "Tasmania"));
+		csp.addConstraint(new MapColoringConstraint(WESTERN, NORTHERN));
+		csp.addConstraint(new MapColoringConstraint(WESTERN, SOUTH));
+		csp.addConstraint(new MapColoringConstraint(SOUTH, NORTHERN));
+		csp.addConstraint(new MapColoringConstraint(QUEENSLAND, NORTHERN));
+		csp.addConstraint(new MapColoringConstraint(QUEENSLAND, SOUTH));
+		csp.addConstraint(new MapColoringConstraint(QUEENSLAND, NEW_SOUTH_WALES));
+		csp.addConstraint(new MapColoringConstraint(NEW_SOUTH_WALES, SOUTH));
+		csp.addConstraint(new MapColoringConstraint(VICTORIA, SOUTH));
+		csp.addConstraint(new MapColoringConstraint(VICTORIA, NEW_SOUTH_WALES));
+		csp.addConstraint(new MapColoringConstraint(VICTORIA, TASMANIA));
 		Map<String, String> solution = csp.backtrackingSearch();
 		if (solution == null) {
 			System.out.println("No solution found!");

CCSPiJ/src/chapter3/SendMoreMoneyConstraint.java

@@ -39,10 +39,18 @@ public boolean satisfied(Map<Character, Integer> assignment) {
 		// if all variables have been assigned, check if it adds correctly
 		if (assignment.size() == letters.size()) {
 			int s = assignment.get('S');
+			// so we don't get answers starting with a 0
+			if (s == 0) {
+				return false;
+			}
 			int e = assignment.get('E');
 			int n = assignment.get('N');
 			int d = assignment.get('D');
 			int m = assignment.get('M');
+			// so we don't get answers starting with a 0
+			if (m == 0) {
+				return false;
+			}
 			int o = assignment.get('O');
 			int r = assignment.get('R');
 			int y = assignment.get('Y');
@@ -60,8 +68,6 @@ public static void main(String[] args) {
 		for (Character letter : letters) {
 			possibleDigits.put(letter, List.of(0, 1, 2, 3, 4, 5, 6, 7, 8, 9));
 		}
-		// so we don't get answers starting with a 0
-		possibleDigits.replace('M', List.of(1));
 		CSP<Character, Integer> csp = new CSP<>(letters, possibleDigits);
 		csp.addConstraint(new SendMoreMoneyConstraint(letters));
 		Map<Character, Integer> solution = csp.backtrackingSearch();