uni/inf2440/hw4/Oblig4.java

abstract class Oblig4 {
	// Required for TegnUt
	int x[];
	int y[];
	int n;
	int MAX_X;
	int MAX_Y;

	IntList coHull;
	NPunkter17 points;
	String name = "Oblig4";

	Oblig4(NPunkter17 points) {
		this.points = points;
		n = points.n;
		x = new int[n];
		y = new int[n];
		coHull = new IntList();
	}

	// Fill x and y arrays
	void fill() {
		points.fyllArrayer(x, y);
	}

	// This method should be overwritten by each implementation.
	// It's responsible for filling in MAX_X, MAX_Y, and coHull
	abstract void solve();

	/*
	 * The rest is utility methods which any implementation will use.
	 */

	// Draw points using TegnUt.
	// Requires x, y, n, MAX_X, MAX_Y, and coHull
	// to be filled out.
	void draw() {
		TegnUt t = new TegnUt(this, coHull, name);
		t.setVisible(true);
	}

	// a, b, and c will be used in the line equation.
	// It doesn't make sense to recalculate them all the time,
	// as they only depend on p1 and p2.
	int lineA(int p1, int p2) {
		return y[p1] - y[p2];
	}
	int lineB(int p1, int p2) {
		return x[p2] - x[p1];
	}
	int lineC(int p1, int p2) {
		return (y[p2] * x[p1]) - (y[p1] * x[p2]);
	}

	// From p1 to p2.
	// == 0: p3 is on the line.
	// > 0: p3 is left of the line.
	// < 0: p3 is right of the line.
	double lineEquation(int a, int b, int c, int p3) {
		return (a * x[p3]) + (b * y[p3]) + c;
	}

	// Distance between two points
	double pointDist(int p1, int p2) {
		int x1 = x[p1], y1 = y[p1];
		int x2 = x[p2], y2 = y[p2];

		int dx = x2 - x1;
		int dy = y2 - y1;
		return Math.abs(Math.sqrt((dx * dx) + (dy * dy)));
	}

	// Distance between the line and p3
	double dist(double l, int a, int b) {
		return l / Math.sqrt((a * a) + (b * b));
	}

	// Create a list of points, in sorted order, on the line
	// given by (a, b, c, p1)
	IntList addPointsOnLine(IntList indexes, int a, int b, int c, int p1) {
		IntList l = new IntList();

		// Add points on the line between p1 and p2
		for (int i = 0; i < indexes.size(); ++i) {
			int idx = indexes.get(i);

			double line = lineEquation(a, b, c, idx);
			if (line == 0)
				l.add(idx);
		}

		// Calculate distances for sorting
		double[] dists = new double[l.size()];
		for (int i = 0; i < l.size(); ++i) {
			dists[i] = pointDist(p1, l.get(i));
		}

		// Sort points based on distance from p1
		// (Bubble sort, but it's usually really few elements)
		boolean sorted;
		do {
			sorted = true;

			// Loop through points, swap non-sorted ones
			for (int i = 1; i < l.size(); ++i) {
				double dist = dists[i];
				double prevDist = dists[i - 1];

				// Skip if already sorted
				if (prevDist <= dist)
					continue;

				sorted = false;

				// Swap indexes
				int tmpi = l.data[i];
				l.data[i] = l.data[i - 1];
				l.data[i - 1] = tmpi;

				// Swap distances
				double tmpd = dists[i];
				dists[i] = dists[i - 1];
				dists[i - 1] = tmpd;
			}
		} while (!sorted);

		return l;
	}
}