Data commit

Task/Hamming-numbers/Java/hamming-numbers-2.java

@@ -0,0 +1,110 @@
+import java.math.BigInteger;
+import java.util.*;
+
+
+public class HammingTriple implements Comparable<HammingTriple> {
+
+    // Precompute a couple of constants that we need all the time
+    private static final BigInteger two = BigInteger.valueOf(2);
+    private static final BigInteger three = BigInteger.valueOf(3);
+    private static final BigInteger five = BigInteger.valueOf(5);
+    private static final double logOf2 = Math.log(2);
+    private static final double logOf3 = Math.log(3);
+    private static final double logOf5 = Math.log(5);
+
+    // The powers of this triple
+    private int a, b, c;
+
+    public HammingTriple(int a, int b, int c) {
+        this.a = a; this.b = b; this.c = c;
+    }
+
+    public String toString() {
+        return "[" + a + ", " + b + ", " + c + "]";
+    }
+
+    public BigInteger getValue() {
+        return two.pow(a).multiply(three.pow(b)).multiply(five.pow(c));
+    }
+
+    public boolean equals(Object other) {
+        if(other instanceof HammingTriple) {
+            HammingTriple h = (HammingTriple) other;
+            return this.a == h.a && this.b == h.b && this.c == h.c;
+        }
+        else { return false; }
+    }
+
+    // Return 0 if this == other, +1 if this > other, and -1 if this < other
+    public int compareTo(HammingTriple other) {
+        // equality
+        if(this.a == other.a && this.b == other.b && this.c == other.c) {
+            return 0;
+        }
+        // this dominates
+        if(this.a >= other.a && this.b >= other.b && this.c >= other.c) {
+            return +1;
+        }
+        // other dominates
+        if(this.a <= other.a && this.b <= other.b && this.c <= other.c) {
+            return -1;
+        }
+
+        // take the logarithms for comparison
+        double log1 = this.a * logOf2 + this.b * logOf3 + this.c * logOf5;
+        double log2 = other.a * logOf2 + other.b * logOf3 + other.c * logOf5;
+
+        // are these different enough to be reliable?
+        if(Math.abs(log1 - log2) > 0.0000001) {
+            return (log1 < log2) ? -1: +1;
+        }
+
+        // oh well, looks like we have to do this the hard way
+        return this.getValue().compareTo(other.getValue());
+        // (getting this far should be pretty rare, though)
+    }
+
+    public static BigInteger computeHamming(int n, boolean verbose) {
+        if(verbose) {
+            System.out.println("Hamming number #" + n);
+        }
+        long startTime = System.currentTimeMillis();
+
+        // The elements of the search frontier
+        PriorityQueue<HammingTriple> frontierQ = new PriorityQueue<HammingTriple>();
+        int maxFrontierSize = 1;
+
+        // Initialize the frontier
+        frontierQ.offer(new HammingTriple(0, 0, 0)); // 1
+
+        while(true) {
+            if(frontierQ.size() > maxFrontierSize) {
+                maxFrontierSize = frontierQ.size();
+            }
+            // Pop out the next Hamming number from the frontier
+            HammingTriple curr = frontierQ.poll();
+
+            if(--n == 0) {
+                if(verbose) {
+                    System.out.println("Time: " + (System.currentTimeMillis() - startTime) + " ms");
+                    System.out.println("Frontier max size: " + maxFrontierSize);
+                    System.out.println("As powers: " + curr.toString());
+                    System.out.println("As value: " + curr.getValue());
+                }
+                return curr.getValue();
+            }
+
+            // Current times five, if at origin in (a,b) plane
+            if(curr.a == 0 && curr.b == 0) {
+                frontierQ.offer(new HammingTriple(curr.a, curr.b, curr.c + 1));
+            }
+            // Current times three, if at line a == 0
+            if(curr.a == 0) {
+                frontierQ.offer(new HammingTriple(curr.a, curr.b + 1, curr.c));
+            }
+            // Current times two, unconditionally
+            curr.a++;
+            frontierQ.offer(curr); // reuse the current HammingTriple object
+        }
+    }
+}