java:puzzlers [Tilialacus]

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<code>
public class HashHistogram {
    static String[] words = {"Man", "skall", "läsa", "javadoc", "innan", "java", "installeras"};
    
    public static void main(String[] args) {
        int[] histogram = new int[5];
        for (String w1: words) {
            for (String w2: words) {
                int hashSum = w1.hashCode() + w2.hashCode();
                histogram[hashSum % histogram.length] ++;
            }
        }
        System.out.print(Arrays.toString(histogram));
    }
}
</code>

  * Kompilerar inte
  * Evig loop
  * Skriver ut histogrammet
  * Något annat

Ok, det fungerade inte. Ah, om hashCode är negativt så blir resultatet negativt. Då gör vi det positivt.

<code>
public class HashHistogram {
    static String[] words = {"Man", "skall", "läsa", "javadoc", "innan", "java", "installeras"};
    
    public static void main(String[] args) {
        int[] histogram = new int[5];
        for (String w1: words) {
            for (String w2: words) {
                int hashSum = w1.hashCode() + w2.hashCode();
                histogram[Math.abs(hashSum) % histogram.length] ++;
            }
        }
        System.out.print(Arrays.toString(histogram));
    }
}
</code>

  * Kompilerar inte
  * Evig loop
  * Skriver ut histogrammet
  * Något annat

  Two component:
  Integer.MIN_VALUE 10000000 00000000 00000000 00000000
  Invert            01111111 11111111 11111111 11111111
  Add 1             10000000 00000000 00000000 00000000


<code>
import java.net.URL;
import java.util.HashSet;
import java.util.Set;

public class UrlEquals {

    static final String[] ADDRESSES = {
        "http://google.com",
        "http://lindsjo.net",
        "http://google.com",
        "http://tilialacus.net",
        "http://google.com",
    };
    
    public static void main(String...args) throws Exception {
        java.security.Security.setProperty("networkaddress.cache.ttl" , "0");
        Set<URL> set = new HashSet<URL>();
        for (String address: ADDRESSES) {
            set.add(new URL(address));
        }
        for (URL url: set) {
            System.out.println(url);
        }
    }
}
</code>


The following code does not work since min + max overflows. Run with -Xmx1200m
<code>
public class AverageInt {
   public static void main(String[] args) {        
        byte[] data = new byte[Integer.MAX_VALUE / 2 + 10];
        System.err.format("Allocated %s elements, %s bytes (%.2fGB)", data.length, data.length, data.length/1024d/1024/1024);
        data[data.length - 1] = Byte.MAX_VALUE;
        find (data, Byte.MAX_VALUE);
    }

    private static void find(byte[] data, byte value) {
        int min = 0;
        int max = data.length - 1;
        int middle = (min + max) / 2;
        while (data[middle] != value && min != max) {
            if (data[middle] < value) {
                min = middle;
            } else {
                max = middle;
            }
            middle = (min + max) / 2;
        }
        System.err.println(min + " " + max + " " + middle);
    }   
}
</code>