101 lines
2.6 KiB
Java
101 lines
2.6 KiB
Java
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/*This is a Java Program to Implement Jarvis Algorithm. Jarvis algorithm or the gift wrapping algorithm is an algorithm for computing the convex hull of a given set of points.*/
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/**
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** Java Program to Implement Jarvis Algorithm
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**/
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import java.util.Scanner;
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import java.util.Arrays;
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/** Class point **/
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class Point
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{
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int x, y;
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}
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/** Class Jarvis **/
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public class Jarvis
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{
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private boolean CCW(Point p, Point q, Point r)
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{
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int val = (q.y - p.y) * (r.x - q.x) - (q.x - p.x) * (r.y - q.y);
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if (val >= 0)
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return false;
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return true;
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}
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public void convexHull(Point[] points)
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{
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int n = points.length;
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/** if less than 3 points return **/
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if (n < 3)
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return;
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int[] next = new int[n];
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Arrays.fill(next, -1);
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/** find the leftmost point **/
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int leftMost = 0;
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for (int i = 1; i < n; i++)
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if (points[i].x < points[leftMost].x)
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leftMost = i;
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int p = leftMost, q;
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/** iterate till p becomes leftMost **/
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do
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{
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/** wrapping **/
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q = (p + 1) % n;
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for (int i = 0; i < n; i++)
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if (CCW(points[p], points[i], points[q]))
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q = i;
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next[p] = q;
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p = q;
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}
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while (p != leftMost);
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/** Display result **/
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display(points, next);
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}
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public void display(Point[] points, int[] next)
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{
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System.out.println("\nConvex Hull points : ");
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for (int i = 0; i < next.length; i++)
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if (next[i] != -1)
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System.out.println("("+ points[i].x +", "+ points[i].y +")");
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}
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/** Main function **/
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public static void main (String[] args)
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{
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Scanner scan = new Scanner(System.in);
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System.out.println("Jarvis Algorithm Test\n");
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/** Make an object of Jarvis class **/
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Jarvis j = new Jarvis();
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System.out.println("Enter number of points n :");
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int n = scan.nextInt();
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Point[] points = new Point[n];
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System.out.println("Enter "+ n +" x, y cordinates");
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for (int i = 0; i < n; i++)
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{
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points[i] = new Point();
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points[i].x = scan.nextInt();
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points[i].y = scan.nextInt();
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}
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j.convexHull(points);
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}
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}
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/*
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Enter number of points n :
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8
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Enter 8 x, y cordinates
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0 3
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4 2
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3 5
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5 3
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3 0
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1 1
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1 2
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2 2
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Convex Hull points :
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(0, 3)
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(3, 5)
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(5, 3)
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(3, 0)
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(1, 1)
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