/src/gov/nih/ncgc/util/GrayCode.java

  1// $Id: GrayCode.java 2707 2009-06-22 09:29:24Z nguyenda $
  2
  3package gov.nih.ncgc.util;
  4
  5import java.util.Observer;
  6import java.util.Observable;
  7
  8// rip this off of wikipedia; knuth's vol. 4 algorithm M doesn't require
  9//   all these auxilary arrays.... don't have it with me right now.
 10public class GrayCode extends Observable {
 11
 12    private int maxsize = 0, size = 0;
 13    private int[] n, g, u, c;
 14
 15    public GrayCode (int N, int k) {
 16	init (N, k);
 17    }
 18
 19    public GrayCode (int[] N) {
 20	init (N);
 21    }
 22
 23    protected void init (int N, int k) {
 24	n = new int[k+1];
 25	g = new int[k+1];
 26	u = new int[k+1];
 27	c = new int[k]; // copy of g
 28
 29	for (int i = 0; i <= k; ++i) {
 30	    g[i] = 0;
 31	    u[i] = 1;
 32	    n[i] = N;
 33	}
 34	size = 0;
 35    }
 36
 37    protected void init (int[] N) {
 38	int k = N.length;
 39	n = new int[k+1];
 40	g = new int[k+1];
 41	u = new int[k+1];
 42	c = new int[k]; // copy of g
 43
 44	int min = Integer.MAX_VALUE;
 45	for (int i = 0; i < k; ++i) {
 46	    g[i] = 0;
 47	    u[i] = 1;
 48	    n[i] = N[i];
 49	    if (N[i] < min) {
 50		min = N[i];
 51	    }
 52	}
 53	g[k] = 0;
 54	u[k] = 1;
 55	n[k] = min;
 56	size = 0;
 57    }
 58
 59    public void generate () {
 60	for(int i, j; g[c.length] == 0;) {
 61	    System.arraycopy(g, 0, c, 0, c.length);
 62
 63	    setChanged ();
 64	    notifyObservers (c);
 65	    
 66	    i = 0; 
 67	    j = g[0] + u[0];
 68	    while (((j >= n[i]) || (j < 0)) && (i < c.length)) {
 69		u[i] = -u[i];
 70		++i;
 71		j = g[i] + u[i];
 72	    }
 73	    g[i] = j;
 74
 75	    ++size;
 76	    if (countObservers() == 0 
 77		|| (maxsize > 0 && size >= maxsize)) {
 78		break;
 79	    }
 80	}
 81    }
 82
 83    public void setMaxSize (int maxsize) {
 84	this.maxsize = maxsize;
 85    }
 86    public int getMaxSize () { return maxsize; }
 87
 88    public int size () { return size; }
 89
 90    public static GrayCode createBinaryGrayCode (int size) {
 91	return new GrayCode (2, size);
 92    }
 93
 94    public static class Enum {
 95        public static void main (final String[] argv) throws Exception {
 96            // all possible subsets = 2^k
 97            GrayCode g = createBinaryGrayCode (argv.length);
 98            g.addObserver(new Observer () {
 99                    public void update (Observable o, Object arg) {
100                        int[] c = (int[])arg;
101                        int j = 0;
102                        for (int i = 0; i < c.length; ++i) {
103                            if (c[i] != 0) {
104                                if (j == 0) {
105                                    System.out.print("[");
106                                }
107                                else if (j > 0) {
108                                    System.out.print(",");
109                                }
110                                System.out.print(argv[i]);
111                                ++j;
112                            }
113                        }
114                        if (j > 0) {
115                            System.out.println("]");
116                        }
117                    }
118                });
119            g.generate();
120        }
121    }
122
123    public static void main (String[] argv) throws Exception {
124	if (argv.length == 0) {
125	    System.out.println("Usage: GrayCode [N k | n0 n1...]\n");
126	    System.exit(1);
127	}
128
129	/*
130	if (argv.length >= 2) {
131	    final int N = Integer.parseInt(argv[0]);
132	    int k = Integer.parseInt(argv[1]);
133
134	    System.out.println("Gray Code ("+N+","+k+")");
135	    GrayCode g = new GrayCode (N, k);
136	    Observer obs = new Observer () {
137		    int index = 0;
138		    public void update (Observable o, Object arg) {
139			int[] c = (int[])arg;
140			System.out.printf("%1$5d: ", ++index);
141			if (N == 2 && c.length < 64) {
142			    long x = 0;
143			    for (int i = 0; i < c.length; ++i) {
144				System.out.print(c[i]+ " ");
145				if (c[i] == 1) {
146				    x |= 1 << (c.length-i-1);
147				}
148			    }
149			    System.out.print("=> "+x);
150			}
151			else {
152			    System.out.print(c[0]);
153			    for (int i = 1; i < c.length; ++i) {
154				System.out.print(" " + c[i]);
155			    }
156			}
157			System.out.println();
158		    }
159		};
160	    g.addObserver(obs);
161	    g.generate();
162	    System.out.println("--");
163	}
164	*/
165
166	int[] a = new int[argv.length];
167	for (int i = 0; i < a.length; ++i) {
168	    a[i] = Integer.parseInt(argv[i]);
169	}
170	GrayCode g = new GrayCode (a);
171	g.addObserver(new Observer () {
172		public void update (Observable o, Object arg) {
173		    int[] c = (int[])arg;
174		    System.out.print(c[0]);
175		    for (int i = 1; i < c.length; ++i) {
176			System.out.print(" " + c[i]);
177		    }
178		    System.out.println();
179		}
180	    });
181	g.generate();
182	System.out.println("** "+g.size()+" values generated!");
183    }
184}