June 2018 Update

Task/Circles-of-given-radius-through-two-points/Java/circles-of-given-radius-through-two-points.java

@@ -0,0 +1,86 @@
+import java.util.Objects;
+
+public class Circles {
+    private static class Point {
+        private final double x, y;
+
+        public Point(Double x, Double y) {
+            this.x = x;
+            this.y = y;
+        }
+
+        public double distanceFrom(Point other) {
+            double dx = x - other.x;
+            double dy = y - other.y;
+            return Math.sqrt(dx * dx + dy * dy);
+        }
+
+        @Override
+        public boolean equals(Object other) {
+            if (this == other) return true;
+            if (other == null || getClass() != other.getClass()) return false;
+            Point point = (Point) other;
+            return x == point.x && y == point.y;
+        }
+
+        @Override
+        public String toString() {
+            return String.format("(%.4f, %.4f)", x, y);
+        }
+    }
+
+    private static Point[] findCircles(Point p1, Point p2, double r) {
+        if (r < 0.0) throw new IllegalArgumentException("the radius can't be negative");
+        if (r == 0.0 && p1 != p2) throw new IllegalArgumentException("no circles can ever be drawn");
+        if (r == 0.0) return new Point[]{p1, p1};
+        if (Objects.equals(p1, p2)) throw new IllegalArgumentException("an infinite number of circles can be drawn");
+        double distance = p1.distanceFrom(p2);
+        double diameter = 2.0 * r;
+        if (distance > diameter) throw new IllegalArgumentException("the points are too far apart to draw a circle");
+        Point center = new Point((p1.x + p2.x) / 2.0, (p1.y + p2.y) / 2.0);
+        if (distance == diameter) return new Point[]{center, center};
+        double mirrorDistance = Math.sqrt(r * r - distance * distance / 4.0);
+        double dx = (p2.x - p1.x) * mirrorDistance / distance;
+        double dy = (p2.y - p1.y) * mirrorDistance / distance;
+        return new Point[]{
+            new Point(center.x - dy, center.y + dx),
+            new Point(center.x + dy, center.y - dx)
+        };
+    }
+
+    public static void main(String[] args) {
+        Point[] p = new Point[]{
+            new Point(0.1234, 0.9876),
+            new Point(0.8765, 0.2345),
+            new Point(0.0000, 2.0000),
+            new Point(0.0000, 0.0000)
+        };
+        Point[][] points = new Point[][]{
+            {p[0], p[1]},
+            {p[2], p[3]},
+            {p[0], p[0]},
+            {p[0], p[1]},
+            {p[0], p[0]},
+        };
+        double[] radii = new double[]{2.0, 1.0, 2.0, 0.5, 0.0};
+        for (int i = 0; i < radii.length; ++i) {
+            Point p1 = points[i][0];
+            Point p2 = points[i][1];
+            double r = radii[i];
+            System.out.printf("For points %s and %s with radius %f\n", p1, p2, r);
+            try {
+                Point[] circles = findCircles(p1, p2, r);
+                Point c1 = circles[0];
+                Point c2 = circles[1];
+                if (Objects.equals(c1, c2)) {
+                    System.out.printf("there is just one circle with center at %s\n", c1);
+                } else {
+                    System.out.printf("there are two circles with centers at %s and %s\n", c1, c2);
+                }
+            } catch (IllegalArgumentException ex) {
+                System.out.println(ex.getMessage());
+            }
+            System.out.println();
+        }
+    }
+}