凸包的JarvisMarch算法——Java语言

public class JarvisMarch<T extends Planarizable>{private List<T> points;private List<T> hull;private static int MAX_ANGLE = 4;   private double currentMinAngle = 0;public JarvisMarch(List<T> points)  {this.points = points;this.hull = new ArrayList<T>();this.calculate();}private void calculate()  {int firstIndex = getFirstPointIndex(this.points);this.hull.clear();this.hull.add(this.points.get(firstIndex));//向list(hull)中添加第一个点currentMinAngle = 0;for (int i = nextIndex(firstIndex, this.points); i != firstIndex; i = nextIndex(i, this.points)) {this.hull.add(this.points.get(i));}//向list(hull)中添加其他的点，这些点将构成一个convex hull}public void remove(T item)  {if (!hull.contains(item)) {points.remove(item);return;}points.remove(item);// TODOcalculate();}public void remove(List<T> items){points.removeAll(items);calculate();}public void add(T item) {points.add(item);List<T> tmplist = new ArrayList<T>();tmplist.addAll(hull);tmplist.add(item);List<T> tmphull = new ArrayList<T>();int firstIndex = getFirstPointIndex(tmplist);tmphull.add(tmplist.get(firstIndex));currentMinAngle = 0;for (int i = nextIndex(firstIndex, tmplist); i != firstIndex; i = nextIndex(i, tmplist)) {tmphull.add(tmplist.get(i));}this.hull = tmphull;}public void add(List<T> items) {points.addAll(items);List<T> tmplist = new ArrayList<T>();tmplist.addAll(hull);tmplist.addAll(items);List<T> tmphull = new ArrayList<T>();int firstIndex = getFirstPointIndex(tmplist);tmphull.add(tmplist.get(firstIndex));currentMinAngle = 0;for (int i = nextIndex(firstIndex, tmplist); i != firstIndex; i = nextIndex(i, tmplist)) {tmphull.add(tmplist.get(i));}this.hull = tmphull;}public List<T> getHull() {return this.hull;}private int nextIndex(int currentIndex, List<T> points) {double minAngle = MAX_ANGLE;double pseudoAngle;int minIndex = 0;for (int i = 0; i < points.size(); i++) {if (i != currentIndex) {pseudoAngle = getPseudoAngle(points.get(i).x() - points.get(currentIndex).x(),points.get(i).y() - points.get(currentIndex).y());if (pseudoAngle >= currentMinAngle && pseudoAngle < minAngle) {minAngle = pseudoAngle;minIndex = i;} else if (pseudoAngle == minAngle) {if ((Math.abs(points.get(i).x()- points.get(currentIndex).x()) > Math.abs(points.get(minIndex).x() - points.get(currentIndex).x()))|| (Math.abs(points.get(i).y()- points.get(currentIndex).y()) > Math.abs(points.get(minIndex).y()- points.get(currentIndex).y()))) {minIndex = i;}}}}currentMinAngle = minAngle;return minIndex;}//获得起始点private int getFirstPointIndex(List<T> points) {int minIndex = 0;for (int i = 1; i < points.size(); i++) {if (points.get(i).y() < points.get(minIndex).y()) {minIndex = i;} else if ((points.get(i).y() == points.get(minIndex).y())&& (points.get(i).x() < points.get(minIndex).x())) {minIndex = i;}}return minIndex;}private double getPseudoAngle(double dx, double dy) {if (dx > 0 && dy >= 0)return dy / (dx + dy);if (dx <= 0 && dy > 0)return 1 + (Math.abs(dx) / (Math.abs(dx) + dy));if (dx < 0 && dy <= 0)return 2 + (dy / (dx + dy));if (dx >= 0 && dy < 0)return 3 + (dx / (dx + Math.abs(dy)));throw new Error("Impossible");}}