uni/inf2440/hw4/NPunkter17.java

import java.util.Random;
/**
* Class NPunkter17 for aa finne n tilfeldige, ulike  punkter i x,y-planet
* ver 7.mai 2015. Reworked to get not cohyll be a square for lage n
************************************************************************/
public class NPunkter17 {
	Random r;
	int n;
	byte [] bitArr;
	static int maxXY, xShift =3;
	int scaleFactor = 3;  // scaleFactor * scaleFactor * n= antall mulige punkter i planet (her: 3*n)
	final  int [] bitMask ={1,2,4,8,16,32,64,128};
	int xCentre =0,yCentre=0, maxVal;

	NPunkter17(int n) {
		this.n =n;
		maxXY = Math.max(10,(int) Math.sqrt(n) * scaleFactor); // største X og Y verdi
		while ((1<<xShift) < maxXY) xShift++;
		xShift = xShift - 3;                    // 8 bits per byte
		bitArr = new byte[(maxXY<<xShift |(maxXY>>3))  + 1];
		r = new Random(123);
		// added to get more 'roundish' set of points
		for (int i = 1 ; i <=20 ; i++){
			xCentre += r.nextInt(maxXY);
			yCentre += r.nextInt(maxXY);
		}
		xCentre /= 20;
		yCentre /= 20;
		maxVal = (int)(xCentre*1.33);
	}

	private void setUsed(int x, int y) {
		bitArr[(x<<xShift) | (y >>3)] |= bitMask[(y&7)];
	}

	private boolean used (int x, int y) {
		return  (bitArr[(x<<xShift) | (y >>3)] & bitMask[y&7]) != 0;
	}

	public void fyllArrayer(int [] x, int[] y) {
		int next =0;
		int xval, yval;
		// new 2017
		while (next < n) {
			do{
				xval = r.nextInt(maxXY)+1;
				yval = r.nextInt(maxXY)+1;
			} while (used (xval, yval) ||
			         Math.abs(xval-xCentre) +Math.abs(yval-yCentre) > maxVal);
			x[next] = xval;
			y[next] = yval;
			setUsed (xval,yval);
			next++;
		} // next point
	}// end fyllArrayer

	public IntList 	lagIntList() {
		IntList res = new IntList(n);
		for (int i= 0; i <n; i++) res.add(i);
		return res;
	}// end fyllArrayer

} // end class NPunkter