improve performance by Hashmap and polynomial function

src/com/github/permatrix/CompactImage.java

@@ -1,6 +1,5 @@
 package com.github.permatrix;
 
-
 import java.awt.Graphics2D;
 import java.awt.image.BufferedImage;
 import java.io.File;
@@ -16,11 +15,15 @@
 
 import javax.imageio.ImageIO;
 
-public class CompactImage {
+public class CompactImage implements Comparable<CompactImage> {
 	int[] dots;
+	int count;
+	private long key;
 
 	public CompactImage(int size) {
 		dots = new int[size];
+		count = 1;
+		key = -1;
 	}
 
 	public void addDot(int x, int y) {
@@ -40,6 +43,10 @@ public List<Dot> getDots() {
 		return dl;
 	}
 
+	/**
+	 * create a new image that is the 90 degree rotation of the image   
+	 * @return
+	 */
 	public CompactImage rotate() {
 		int dim = dots.length;
 		CompactImage ni = new CompactImage(dim);
@@ -51,6 +58,9 @@ public CompactImage rotate() {
 		return ni;
 	}
 
+	/**
+	 * rotate the image by 90 degree, and re-use this object
+	 */
 	public void rotateSelf() {
 		int dim = dots.length;
 		int[] shadow = new int[dim];
@@ -60,10 +70,47 @@ public void rotateSelf() {
 			shadow[x1] = y1;
 		}
 		System.arraycopy(shadow, 0, dots, 0, dim);
+		key = -1;
+	}
+
+	/**
+	 * calculate an unique key for each image by using polynomial. 
+	 * @return
+	 */
+	private static final int P_PRIME = 19;
+	public long imageKey() {
+		if (key == -1) {
+			key = 0;
+			long poly = 1;
+			for (int x = 0; x < dots.length; x++) {
+				key += dots[x] * poly;
+				poly *= P_PRIME;
+			}
+		}
+		return key;
+	}
+
+	@Override
+	public int hashCode() {
+		return (int) key;
 	}
 
-	public boolean equals(CompactImage img) {
+	@Override
+	public boolean equals(Object obj) {
+		CompactImage img = (CompactImage) obj;
+		return imageKey() == img.imageKey();
+	}
+
+	/**
+	 * Compare two Image by compare each dot, slowest method
+	 * 
+	 * @param img
+	 * @return True - when two images are equal; False - when two images are not
+	 *         same
+	 */
+	public boolean compareWith(CompactImage img) {
 		assert (img != null);
+
 		int dim = dots.length;
 		if (dim != img.dots.length)
 			return false;
@@ -82,7 +129,10 @@ public CompactImage clone() {
 		return ni;
 	}
 
-	// imprint rotated images
+	/**
+	 * imprint 3 rotated images with original and put all dots in a collection.
+	 * @return
+	 */
 	public Collection<Dot> imprint() {
 		TreeSet<Dot> ts = new TreeSet<Dot>();
 		ts.addAll(getDots());
@@ -95,6 +145,10 @@ public Collection<Dot> imprint() {
 		return ts;
 	}
 
+	/**
+	 * draw the visual representation of the image in Ascii graphics
+	 * @param pw
+	 */
 	public void visualize(PrintStream pw) {
 		int dim = dots.length;
 		char[][] visual = new char[dim][dim];
@@ -111,11 +165,14 @@ public void visualize(PrintStream pw) {
 			pw.println();
 		}
 	}
-
+
+	/**
+	 * generate the PNG graphics representation of the image and save to file
+	 */
 	public void visualize() {
 		int dim = dots.length;
-		int width = dim * 17 + 1; 
-		BufferedImage img = new BufferedImage(width,width,BufferedImage.TYPE_INT_RGB);
+		int width = dim * 17 + 1;
+		BufferedImage img = new BufferedImage(width, width, BufferedImage.TYPE_INT_RGB);
 		Graphics2D g2d = img.createGraphics();
 		visualize(0, 0, 17, g2d);
 		try {
@@ -128,16 +185,29 @@ public void visualize() {
 		g2d.dispose();
 	}
 
+	/**
+	 * draw the graphic representation of the image in a graphic device
+	 * @param posX
+	 * @param posY
+	 * @param gridSize
+	 * @param g2d
+	 */
 	public void visualize(int posX, int posY, int gridSize, Graphics2D g2d) {
 		int dim = dots.length;
 		int width = dim * gridSize + 1;
 		g2d.drawRect(posX, posY, width - 1, width - 1);
-		for(int step = dim - 1; step >= 0; step--) {
+		for (int step = dim - 1; step >= 0; step--) {
 			g2d.drawLine(posX, posY + step * gridSize, posX + width - 1, posY + step * gridSize);
 			g2d.drawLine(posX + step * gridSize, posY, posX + step * gridSize, posY + width - 1);
 		}
 		for (int x = 0; x < dim; x++) {
 			g2d.fillRect(posX + x * gridSize + 1, posY + dots[x] * gridSize + 1, gridSize - 1, gridSize - 1);
 		}
 	}
+
+	@Override
+	public int compareTo(CompactImage img) {
+		return (int)(key - img.key);
+	}
+
 }

src/com/github/permatrix/DictOrderPermutator.java

@@ -83,4 +83,24 @@ private static long getFactorial(int n) {
 		}
 		return fact;
 	}
+
+	/**
+	 * A test method of the permutation generator
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		DictOrderPermutator pc = new DictOrderPermutator(4);
+		while (pc.hasNext()) {
+			int[] dots = pc.next();
+			long hash = 0;
+			long poly = 1;
+			for (int x = 0; x < dots.length; x++) {
+				System.out.print(dots[x]);
+				hash += dots[x] * poly;
+				poly *= 11;
+
+			}
+			System.out.println(" => " + hash);
+		}
+	}
 }