BruteCollinearPoints.java

import java.util.*;
import edu.princeton.cs.algs4.*;

public class BruteCollinearPoints {

    private ArrayList<LineSegment> segs;

    public BruteCollinearPoints(Point[] points) {

        if (points == null) {
            throw new java.lang.NullPointerException();
        }

        Point[] copyPoints = Arrays.copyOf(points, points.length);

        Arrays.sort(copyPoints);
        checkDuplicatePoints(copyPoints);
        segs = new ArrayList<LineSegment>();


        for (int i = 0; i < copyPoints.length - 3; i++) {
            Point p = copyPoints[i];
            if (p == null) {
                throw new java.lang.NullPointerException();
            }
            for (int j = i + 1; j < copyPoints.length - 2; j++) {
                Point q = copyPoints[j];
                if (q == null) {
                    throw new java.lang.NullPointerException();
                }
                for (int k = j + 1; k < copyPoints.length - 1; k++) {
                    Point r = copyPoints[k];
                    if (r == null) {
                        throw new java.lang.NullPointerException();
                    }
                    for (int l = k + 1; l < copyPoints.length; l++) {
                        Point s = copyPoints[l];
                        if (s == null) {
                            throw new java.lang.NullPointerException();
                        }
                        double pq = p.slopeTo(q);
                        double pr = p.slopeTo(r);
                        double ps = p.slopeTo(s);

                        if (pq == pr && pq == ps && pr == ps) {
                            segs.add(new LineSegment(p, s));
                        }
                    }
                }
            }
        }
    }

    private void checkDuplicatePoints(Point[] points) {

        for (int i = 1; i < points.length; i++) {
            if (points[i].compareTo(points[i - 1]) == 0) {
                throw new java.lang.IllegalArgumentException();
            }
        }
    }

    public           int numberOfSegments() {
        return segs.size();
    }
    public LineSegment[] segments() {
        return segs.toArray(new LineSegment[segs.size()]);
    }


    public static void main(String[] args) {

        // read the n points from a file
        String s = "/home/hepeng/Algorithm(4th)/Coursera/Collinear Points/collinear/repeat";
        In in = new In(s);
        int n = in.readInt();
        Point[] points = new Point[n];
        for (int i = 0; i < n; i++) {
            int x = in.readInt();
            int y = in.readInt();
            points[i] = new Point(x, y);
        }

        // draw the points
        StdDraw.enableDoubleBuffering();
        StdDraw.setXscale(0, 32768);
        StdDraw.setYscale(0, 32768);
        for (Point p : points) {
            p.draw();
        }
        StdDraw.show();

        // print and draw the line segments
        BruteCollinearPoints collinear = new BruteCollinearPoints(points);
        for (LineSegment segment : collinear.segments()) {
            StdOut.println(segment);
            segment.draw();
        }
        StdDraw.show();
    }
}