Jarvis March Algorithm in Java

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.

Here is the source code of the Java Program to Implement Jarvis Algorithm. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

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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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    }
```

    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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        } 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 : ");

        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);

        System.out.println("Jarvis Algorithm Test\n");

        /** Make an object of Jarvis class **/

        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();

            points[i].y = scan.nextInt();

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        }        
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        j.convexHull(points);        
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    }
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}
```

Jarvis Algorithm Test
 
Enter number of points n :
8
Enter 8 x, y cordinates
0 3
4 2
3 5
5 3
3 0
1 1
1 2
2 2
 
Convex Hull points :
(0, 3)
(3, 5)
(5, 3)
(3, 0)
(1, 1)

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