bin-vector sphere

BinVectorSphere.java

import java.util.BitSet;
import java.util.Objects;
import java.util.Scanner;
import java.util.function.Supplier;
import java.util.stream.Stream;

import static java.lang.System.out;

public class BinVectorSphere {
    public static void main(String[] args) {
        final Scanner scanner = new Scanner(System.in);

        out.println("Enter length");
        final int length = scanner.nextInt();
        if (length < 0) throw new IllegalArgumentException("Length cannot be negative");

        scanner.nextLine();
        out.println("Enter center");
        final BitSet center = readBitVector(length, scanner);

        out.println("Enter radius");
        final int radius = scanner.nextInt();
        if (radius < 0) throw new IllegalArgumentException("Radius cannot be negative");

        out.print("S(");
        printBits(length, center);
        out.println(", " + radius + ") = {");
        sphere(length, center, radius)
                .takeWhile(Objects::nonNull)
                .forEach(vector -> {
                    out.print('\t');
                    printBits(length, vector);
                    out.println();
                });
        out.println('}');
    }

    private static BitSet readBitVector(final int length, final Scanner scanner) {
        final String line = scanner.nextLine();
        if (line.length() != length) throw new IllegalArgumentException("vector should be of " + length + " bits");

        final BitSet bitSet = new BitSet(length);
        for (int i = 0; i < length; i++) {
            final char character = line.charAt(i);
            if (character == '1') bitSet.set(i);
            else if (character != '0') throw new IllegalArgumentException("A vector should be written using 0s and 1s");
        }

        return bitSet;
    }

    private static void printBits(final int length, final BitSet bitSet) {
        for (int i = 0; i < length; i++) out.print(bitSet.get(i) ? '1' : '0');
    }

    private static Stream<BitSet> sphere(final int length, final BitSet center, final int radius) {
        return Stream.generate(SphereGenerator.create(length, center, radius));
    }

    private static final class SphereGenerator implements Supplier<BitSet> {

        private final int length;
        private final BitSet center;
        private BitSet radiusVector;

        public SphereGenerator(final int length, final BitSet center, final BitSet radiusVector) {
            this.length = length;
            this.center = center;
            this.radiusVector = radiusVector;
        }

        @Override
        public BitSet get() {
            if (radiusVector == null) return null;

            final BitSet result = (BitSet) center.clone();
            result.xor(radiusVector);

            incrementRadiusVector();

            return result;
        }

        private void incrementRadiusVector() {
            for (int index = length - 2; index >= 0; --index) {
                if (radiusVector.get(index)) { // try move to the right
                    final int nextIndex;
                    if (radiusVector.get(nextIndex = index + 1)) {
                        continue; // cannot move to the right
                    }

                    radiusVector.clear(index);
                    radiusVector.set(nextIndex);
                    return;
                }
            }

            radiusVector = null;
        }

        public static Supplier<BitSet> create(final int length, final BitSet center, final int radius) {
            if (radius > length) throw new IllegalArgumentException("Radius cannot be greater than n");

            BitSet radiusVector = new BitSet();
            for (int i = 0; i < radius; i++) radiusVector.set(i);

            return new SphereGenerator(length, center, radiusVector);
        }
    }
}

example-1.log

Enter length
6
Enter center
000000
Enter radius
3
S(000000, 3) = {
	111000
	110100
	110010
	110001
	101001
	100101
	100011
	010011
	001011
	000111
}

example-2.log

Enter length
10
Enter center
1100110011
Enter radius
5
S(1100110011, 5) = {
	0011010011
	0011100011
	0011111011
	0011110111
	0011110001
	0011110010
	0010010010
	0010100010
	0010111010
	0010110110
	0010110000
	0001110000
	0000010000
	0000100000
	0000111000
	0000110100
	0110110100
	0101110100
	0100010100
	0100100100
	0100111100
	1000111100
	1110111100
	1101111100
	1100011100
	1100101100
}

example-3.log

Enter length
20
Enter center
10011010100101010110
Enter radius
7
S(10011010100101010110, 7) = {
	01100100100101010110
	01100111100101010110
	01100110000101010110
	01100110110101010110
	01100110101101010110
	01100110100001010110
	01100110100111010110
	01100110100100010110
	01100110100101110110
	01100110100101000110
	01100110100101011110
	01100110100101010010
	01100110100101010100
	01100110100101010111
	01100000100101010111
	01100011100101010111
	01100010000101010111
	01100010110101010111
	01100010101101010111
	01100010100001010111
	01100010100111010111
	01100010100100010111
	01100010100101110111
	01100010100101000111
	01100010100101011111
	01100010100101010011
	01100010100101010101
	01101110100101010101
	01101000100101010101
	01101011100101010101
	01101010000101010101
	01101010110101010101
	01101010101101010101
	01101010100001010101
	01101010100111010101
	01101010100100010101
	01101010100101110101
	01101010100101000101
	01101010100101011101
	01101010100101010001
	01110010100101010001
	01111110100101010001
	01111000100101010001
	01111011100101010001
	01111010000101010001
	01111010110101010001
	01111010101101010001
	01111010100001010001
	01111010100111010001
	01111010100100010001
	01111010100101110001
	01111010100101000001
	01111010100101011001
	01001010100101011001
	01010010100101011001
	01011110100101011001
	01011000100101011001
	01011011100101011001
	01011010000101011001
	01011010110101011001
	01011010101101011001
	01011010100001011001
	01011010100111011001
	01011010100100011001
	01011010100101111001
	01011010100101001001
	00111010100101001001
	00001010100101001001
	00010010100101001001
	00011110100101001001
	00011000100101001001
	00011011100101001001
	00011010000101001001
	00011010110101001001
	00011010101101001001
	00011010100001001001
	00011010100111001001
	00011010100100001001
	00011010100101101001
	11011010100101101001
	10111010100101101001
	10001010100101101001
	10010010100101101001
	10011110100101101001
	10011000100101101001
	10011011100101101001
	10011010000101101001
	10011010110101101001
	10011010101101101001
	10011010100001101001
	10011010100111101001
	10011010100100101001
}