Jarvis March Implementation in Java

CONTRIBUTORS.md

@@ -1,4 +1,4 @@
-This file lists everyone, who contributed to this repo and wanted to show up here. If you're looking for information on contribution, please check the `CONTRIBUTING.md` out.
+This file lists everyone, who contributed to this repo and wanted to show up here. If you're looking for information on contribution, please check the `CONTRIBUTING.md` out.
 
 # Contributors
 
@@ -37,3 +37,4 @@ This file lists everyone, who contributed to this repo and wanted to show up her
 - Ken Power
 - PaddyKe
 - nic-hartley
+- crafter312

contents/jarvis_march/code/java/JarvisMarch.java

@@ -0,0 +1,111 @@
+import java.util.*;
+
+public class JarvisMarch {
+
+ static class Point {
+ private double x;
+ private double y;
+
+ public Point(double a, double b) {
+ x = a;
+ y = b;
+ }
+
+ public double getX() {
+ return x;
+ }
+ public double getY() {
+ return y;
+ }
+
+ public boolean equals(Point p) {
+ if (p.getX() == x && p.getY() == y) {
+ return true;
+ } else {
+ return false;
+ }
+ }
+ public double magnitude() {
+ return Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
+ }
+ }
+
+ //find the angle by creating two vectors and then using a property of dot products
+ private static double angle(Point a, Point b, Point c) {
+ Point ab = new Point(b.getX() - a.getX(), b.getY() - a.getY());
+ Point bc = new Point(c.getX() - b.getX(), c.getY() - b.getY());
+ return Math.acos(-1 * ((ab.getX() * bc.getX()) + (ab.getY() * bc.getY())) /
+ (ab.magnitude() * bc.magnitude()));
+ }
+
+ public static ArrayList<Point> jarvisMarch(ArrayList<Point> arr) {
+ ArrayList<Point> hull = new ArrayList<Point>();
+ Point pointOnHull = new Point(Double.MAX_VALUE, 0);
+
+ //find leftmost point
+ for (Point p: arr) {
+ if (p.getX() < pointOnHull.getX()) {
+ pointOnHull = p;
+ }
+ }
+ hull.add(pointOnHull);
+
+ //look for the rest of the points on the hull
+ Point ref;
+ while (true) {
+ if (hull.size() == 1) {
+ ref = new Point(pointOnHull.getX(), pointOnHull.getY() + 1); //finds a third point to use in calculating the angle
+ } else {
+ ref = hull.get(hull.size() - 2);
+ }
+ Point endpoint = arr.get(0); //initial canidate for next point in hull
+ for (Point p: arr) {
+ if (angle(p, pointOnHull, ref) > angle(endpoint, pointOnHull, ref)) { //found a point that makes a greater angle
+ endpoint = p;
+ }
+ }
+ pointOnHull = endpoint;
+ if (pointOnHull.equals(hull.get(0))) { //add next point to hull if not equal to the leftmost point
+ break;
+ } else {
+ hull.add(pointOnHull);
+ }
+ }
+ return hull;
+ }
+
+ public static void main(String[] args) {
+
+ //test array setup
+ ArrayList<Point> gift = new ArrayList<Point>();
+ gift.add(new Point(-5, 2));
+ gift.add(new Point(5, 7));
+ gift.add(new Point(-6, -12));
+ gift.add(new Point(-14, -14));
+ gift.add(new Point(9, 9));
+ gift.add(new Point(-1, -1));
+ gift.add(new Point(-10, 11));
+ gift.add(new Point(-6, 15));
+ gift.add(new Point(-6, -8));
+ gift.add(new Point(15, -9));
+ gift.add(new Point(7, -7));
+ gift.add(new Point(-2, -9));
+ gift.add(new Point(6, -5));
+ gift.add(new Point(0, 14));
+ gift.add(new Point(2, 8));
+
+ //print initial array of points
+ System.out.println("Gift:");
+ for (Point p: gift) {
+ System.out.println("[" + p.getX() + ", " + p.getY() + "]");
+ }
+
+ //find and print the array of points in the hull
+ ArrayList<Point> hull = jarvisMarch(gift);
+ System.out.println("Wrapping:");
+ for (Point p: hull) {
+ System.out.println("[" + p.getX() + ", " + p.getY() + "]");
+ }
+ }
+
+}

contents/jarvis_march/jarvis_march.md

@@ -40,6 +40,8 @@ Since this algorithm, there have been many other algorithms that have advanced t
 [import, lang:"python"](code/python/jarvisMarch.py)
 {% sample lang="cpp" %}
 [import, lang:"c_cpp"](code/c++/jarvis_march.cpp)
+{% sample lang="java" %}
+[import, lang:"java"](code/java/JarvisMarch.java)
 {% sample lang="go" %}
 [import, lang:"go"](code/golang/jarvis.go)
 {% endmethod %}