``` 001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099 100 101 ``` ```package algs9; // section 9.8 import algs12.Point2D; import stdlib.*; /* *********************************************************************** * Compilation: javac FarthestPair.java * Execution: java FarthestPair < input.txt * Dependencies: GrahamScan.java Point2D.java * * Given a set of N points in the plane, find the farthest pair * (equivalently, compute the diameter of the set of points). * * Computes the convex hull of the set of points and using the * rotating callipers method to find all antipodal point pairs * and the farthest pair. * * % java FarthestPair < rs1423.txt * 7748.838622658237 from (24690.0, 216.0) to (32420.0, 756.0) *************************************************************************/ public class FarthestPair { // farthest pair of points and distance private Point2D best1, best2; private double bestDistance = Double.NEGATIVE_INFINITY; public FarthestPair(Point2D[] points) { GrahamScan graham = new GrahamScan(points); // single point if (points.length <= 1) return; // number of points on the hull int M = 0; for (Point2D p : graham.hull()) M++; // the hull, in counterclockwise order Point2D[] hull = new Point2D[M+1]; int m = 1; for (Point2D p : graham.hull()) { hull[m++] = p; } // all points are equal if (M == 1) return; // points are collinear if (M == 2) { best1 = hull[1]; best2 = hull[2]; bestDistance = best1.distanceTo(best2); return; } // k = farthest vertex from edge from hull[1] to hull[M] int k = 2; while (Point2D.area2(hull[M], hull[k+1], hull[1]) > Point2D.area2(hull[M], hull[k], hull[1])) { k++; } int j = k; for (int i = 1; i <= k; i++) { // StdOut.println("hull[i] + " and " + hull[j] + " are antipodal"); if (hull[i].distanceTo(hull[j]) > bestDistance) { best1 = hull[i]; best2 = hull[j]; bestDistance = hull[i].distanceTo(hull[j]); } while ((j < M) && Point2D.area2(hull[i], hull[j+1], hull[i+1]) > Point2D.area2(hull[i], hull[j], hull[i+1])) { j++; // StdOut.println(hull[i] + " and " + hull[j] + " are antipodal"); double distance = hull[i].distanceTo(hull[j]); if (distance > bestDistance) { best1 = hull[i]; best2 = hull[j]; bestDistance = hull[i].distanceTo(hull[j]); } } } } public Point2D either() { return best1; } public Point2D other() { return best2; } public double distance() { return bestDistance; } public static void main(String[] args) { StdIn.fromFile ("data/rs1423.txt"); int N = StdIn.readInt(); Point2D[] points = new Point2D[N]; for (int i = 0; i < N; i++) { int x = StdIn.readInt(); int y = StdIn.readInt(); points[i] = new Point2D(x, y); } FarthestPair farthest = new FarthestPair(points); StdOut.println(farthest.distance() + " from " + farthest.either() + " to " + farthest.other()); } } ```