Merge pull request #113 from Divyesh000/PolygonCalculator

create a PolygonCalculator class

src/main/java/com/github/creme332/algorithms/PolygonCalculator.java

@@ -0,0 +1,68 @@
+package com.github.creme332.algorithms;
+
+import java.awt.Polygon;
+import java.awt.Shape;
+import java.awt.geom.Point2D;
+import java.util.HashMap;
+import java.util.Map;
+
+public class PolygonCalculator {
+
+    private final Map<Integer, Shape> polygonCache = new HashMap<>();
+
+    public Point2D.Double rotateVector(Point2D.Double point, double radAngle) {
+        return new Point2D.Double(
+            point.x * Math.cos(radAngle) - point.y * Math.sin(radAngle),
+            point.x * Math.sin(radAngle) + point.y * Math.cos(radAngle)
+        );
+    }
+
+    private Shape getRegularPolygon(int sidesCount, int length) {
+        if (polygonCache.containsKey(sidesCount)) {
+            return polygonCache.get(sidesCount);
+        }
+
+        double rotationAngle = Math.toRadians(360.0 / sidesCount);
+        Point2D.Double[] points = new Point2D.Double[sidesCount];
+
+        points[0] = new Point2D.Double(
+            length * Math.sin(rotationAngle / 2),
+            length * Math.cos(rotationAngle / 2)
+        );
+
+        for (int i = 1; i < sidesCount; i++) {
+            Point2D.Double vector = new Point2D.Double(points[i - 1].x, points[i - 1].y);
+            Point2D.Double rotatedVector = rotateVector(vector, rotationAngle);
+            points[i] = new Point2D.Double(rotatedVector.x, rotatedVector.y);
+        }
+
+        int[] x = new int[sidesCount];
+        int[] y = new int[sidesCount];
+        for (int i = 0; i < sidesCount; i++) {
+            x[i] = (int) Math.round(points[i].x);
+            y[i] = (int) Math.round(points[i].y);
+        }
+
+        Polygon polygon = new Polygon(x, y, sidesCount);
+        polygonCache.put(sidesCount, polygon);
+        return polygon;
+    }
+
+    public int[][] getOrderedPoints(int sidesCount, int length) {
+        Shape polygon = getRegularPolygon(sidesCount, length);
+        Polygon poly = (Polygon) polygon;
+
+        int[] xPoints = poly.xpoints;
+        int[] yPoints = poly.ypoints;
+        int nPoints = poly.npoints;
+
+        int[] xOrdered = new int[nPoints];
+        int[] yOrdered = new int[nPoints];
+        for (int i = 0; i < nPoints; i++) {
+            xOrdered[i] = xPoints[i];
+            yOrdered[i] = yPoints[i];
+        }
+
+        return new int[][] { xOrdered, yOrdered };
+    }
+}