38 lines
1.3 KiB
Java
38 lines
1.3 KiB
Java
import java.math.BigInteger;
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import java.util.PriorityQueue;
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final class Hamming {
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private static BigInteger THREE = BigInteger.valueOf(3);
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private static BigInteger FIVE = BigInteger.valueOf(5);
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private static void updateFrontier(BigInteger x,
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PriorityQueue<BigInteger> pq) {
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pq.offer(x.shiftLeft(1));
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pq.offer(x.multiply(THREE));
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pq.offer(x.multiply(FIVE));
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}
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public static BigInteger hamming(int n) {
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if (n <= 0)
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throw new IllegalArgumentException("Invalid parameter");
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PriorityQueue<BigInteger> frontier = new PriorityQueue<BigInteger>();
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updateFrontier(BigInteger.ONE, frontier);
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BigInteger lowest = BigInteger.ONE;
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for (int i = 1; i < n; i++) {
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lowest = frontier.poll();
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while (frontier.peek().equals(lowest))
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frontier.poll();
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updateFrontier(lowest, frontier);
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}
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return lowest;
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}
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public static void main(String[] args) {
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System.out.print("Hamming(1 .. 20) =");
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for (int i = 1; i < 21; i++)
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System.out.print(" " + hamming(i));
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System.out.println("\nHamming(1691) = " + hamming(1691));
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System.out.println("Hamming(1000000) = " + hamming(1000000));
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}
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}
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