get Random Unset Bit - Java Language Basics

Java examples for Language Basics:Bit

  1. HOME
  2. Java
  3. Language Basics
  4. Bit

Description

get Random Unset Bit

Demo Code

/*/*from w w  w.  ja v  a2 s.  co  m*/
 This file is part of p300.


 p300 is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 p300 is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with p300.  If not, see <http://www.gnu.org/licenses/>.
 */
import java.util.BitSet;

public class Main{
    public static int getRandomUnsetBit(BitSet bs, int len) {
        if (bs.cardinality() >= len) {
            // failure
            return 0;
        }

        // try 20 times to see a random one
        for (int i = 0; i < 20; i++) {
            int idx = RandomGenerator.getInt(0, len);

            if (!bs.get(idx))
                return idx;
        }

        // trying randomly did not work      
        int numberOfUnsetBits = len - bs.cardinality();
        int numberOfUnsetBitToPick = RandomGenerator.getInt(0,
                numberOfUnsetBits);

        int j = numberOfUnsetBitToPick;
        for (int i = 0; i < len; i++) {
            if (!bs.get(i)) {
                // unset bit
                j--;

                if (j <= 0) {
                    //D.out("-- random chunk pick " + numberOfUnsetBitToPick + " -> " + i);
                    return i;
                }
            }
        }

        // should not happen
        //D.out ("Picked chunk 0");
        return 0;

    }
}

Related Tutorials