1 files changed, 77 insertions, 0 deletions
diff --git a/src/jrummikub/ai/fdsolver/constraint/OffsetConstraint.java b/src/jrummikub/ai/fdsolver/constraint/OffsetConstraint.java
new file mode 100644
index 0000000..f91dcda
--- /dev/null
+++ b/src/jrummikub/ai/fdsolver/constraint/OffsetConstraint.java
@@ -0,0 +1,77 @@
+package jrummikub.ai.fdsolver.constraint;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Iterator;
+
+import jrummikub.ai.fdsolver.Constraint;
+import jrummikub.ai.fdsolver.Propagator;
+import jrummikub.ai.fdsolver.Satisfiability;
+import jrummikub.ai.fdsolver.Var;
+
+public class OffsetConstraint implements Constraint {
+	private Var<Integer> x, y;
+	int offset;
+	Propagator propX, propY;
+
+	public OffsetConstraint(int offset, Var<Integer> x, Var<Integer> y) {
+		this.offset = offset;
+		this.x = x;
+		this.y = y;
+		propX = new OffsetProp(offset, x, y);
+		propY = new OffsetProp(-offset, y, x);
+	}
+
+	@Override
+	public Collection<Var<?>> getWatchedVars() {
+		return Arrays.<Var<?>> asList(x, y);
+	}
+	
+	private class OffsetProp implements Propagator {
+		private Var<Integer> x, y;
+		private int offset;
+		public OffsetProp(int offset, Var<Integer> x, Var<Integer> y) {
+			this.offset = offset;
+			this.x = x;
+			this.y = y;
+		}
+		
+		@Override
+		public Collection<Var<?>> getWatchedVars() {
+			return Arrays.<Var<?>>asList(y);
+		}
+
+		@Override
+		public void propagate() {
+			for(Iterator<Integer> i = x.iterator(); i.hasNext();) {
+				if(!y.getRange().contains(i.next() + offset)) {
+					i.remove();
+				}
+			}
+		}
+	}
+	
+
+	@Override
+	public Collection<Propagator> getPropagators(boolean negate) {
+		return Arrays.asList(propX, propY);
+	}
+
+	@Override
+	public Satisfiability getSatisfiability() {
+		HashSet<Integer> shiftedRange = new HashSet<Integer>();
+		for (int val : x.getRange()) {
+			shiftedRange.add(val + offset);
+		}
+		shiftedRange.retainAll(y.getRange());
+		if (shiftedRange.isEmpty()) {
+			return Satisfiability.UNSAT;
+		} else if (x.getRange().size() == 1 && y.getRange().size() == 1) {
+			return Satisfiability.TAUT;
+		} else {
+			return Satisfiability.SAT;
+		}
+	}
+
+}