Given a set of points in the plane. the convex hull of the set is the smallest convex polygon that contains all the points of it.
https://www.geeksforgeeks.org/convex-hull-set-1-jarviss-algorithm-or-wrapping/
Lin家
Java:
// Java program to find convex hull of a set of points. Refer // https://www.geeksforgeeks.org/orientation-3-ordered-points/ // for explanation of orientation() import java.util.*; class Point { int x, y; Point(int x, int y){ this.x=x; this.y=y; } } class GFG { // To find orientation of ordered triplet (p, q, r). // The function returns following values // 0 --> p, q and r are colinear // 1 --> Clockwise // 2 --> Counterclockwise public static int orientation(Point p, Point q, Point r) { int val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y); if (val == 0) return 0; // collinear return (val > 0)? 1: 2; // clock or counterclock wise } // Prints convex hull of a set of n points. public static void convexHull(Point points[], int n) { // There must be at least 3 points if (n < 3) return; // Initialize Result Vector<Point> hull = new Vector<Point>(); // Find the leftmost point int l = 0; for (int i = 1; i < n; i++) if (points[i].x < points[l].x) l = i; // Start from leftmost point, keep moving // counterclockwise until reach the start point // again. This loop runs O(h) times where h is // number of points in result or output. int p = l, q; do { // Add current point to result hull.add(points[p]); // Search for a point ‘q‘ such that // orientation(p, x, q) is counterclockwise // for all points ‘x‘. The idea is to keep // track of last visited most counterclock- // wise point in q. If any point ‘i‘ is more // counterclock-wise than q, then update q. q = (p + 1) % n; for (int i = 0; i < n; i++) { // If i is more counterclockwise than // current q, then update q if (orientation(points[p], points[i], points[q]) == 2) q = i; } // Now q is the most counterclockwise with // respect to p. Set p as q for next iteration, // so that q is added to result ‘hull‘ p = q; } while (p != l); // While we don‘t come to first // point // Print Result for (Point temp : hull) System.out.println("(" + temp.x + ", " + temp.y + ")"); } /* Driver program to test above function */ public static void main(String[] args) { Point points[] = new Point[7]; points[0]=new Point(0, 3); points[1]=new Point(2, 3); points[2]=new Point(1, 1); points[3]=new Point(2, 1); points[4]=new Point(3, 0); points[5]=new Point(0, 0); points[6]=new Point(3, 3); int n = points.length; convexHull(points, n); } }
原文地址:https://www.cnblogs.com/lightwindy/p/9744073.html
时间: 2024-11-06 09:44:58