Task: Hailstone sequence





Java: import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

class Hailstone {

  public static List<Long> getHailstoneSequence(long n) {
    if (n <= 0)
      throw new IllegalArgumentException("Invalid starting sequence number");
    List<Long> list = new ArrayList<Long>();
    list.add(Long.valueOf(n));
    while (n != 1) {
      if ((n & 1) == 0)
        n = n / 2;
      else
        n = 3 * n + 1;
      list.add(Long.valueOf(n));
    }
    return list;
  }
  
  public static void main(String[] args) {
    List<Long> sequence27 = getHailstoneSequence(27);
    System.out.println("Sequence for 27 has " + sequence27.size() + " elements: " + sequence27);
    
    long MAX = 100000;
    
    {
      long highestNumber = 1;
      int highestCount = 1;
      for (long i = 2; i < MAX; i++) {
        int count = getHailstoneSequence(i).size();
        if (count > highestCount) {
          highestCount = count;
          highestNumber = i;
        }
      }
      System.out.println("Method 1, number " + highestNumber + " has the longest sequence, with a length of " + highestCount);
    }
    
    
    {
      long highestNumber = 1;
      int highestCount = 1;
      for (long i = 2; i < MAX; i++) {
        int count = 1;
        long n = i;
        while (n != 1) {
          if ((n & 1) == 0)
            n = n / 2;
          else
            n = 3 * n + 1;
          count++;
        }
        if (count > highestCount) {
          highestCount = count;
          highestNumber = i;
        }
      }
      System.out.println("Method 2, number " + highestNumber + " has the longest sequence, with a length of " + highestCount);
    }
    
    
    {
      long highestNumber = 1;
      long highestCount = 1;
      Map<Long, Integer> sequenceMap = new HashMap<Long, Integer>();
      sequenceMap.put(Long.valueOf(1), Integer.valueOf(1));
      
      List<Long> currentList = new ArrayList<Long>();
      for (long i = 2; i < MAX; i++) {
        currentList.clear();
        Long n = Long.valueOf(i);
        Integer count = null;
        while ((count = sequenceMap.get(n)) == null) {
          currentList.add(n);
          long nValue = n.longValue();
          if ((nValue & 1) == 0)
            n = Long.valueOf(nValue / 2);
          else
            n = Long.valueOf(3 * nValue + 1);
        }
        int curCount = count.intValue();
        for (int j = currentList.size() - 1; j >= 0; j--)
          sequenceMap.put(currentList.get(j), Integer.valueOf(++curCount));
        if (curCount > highestCount) {
          highestCount = curCount;
          highestNumber = i;
        }
      }
      System.out.println("Method 3, number " + highestNumber + " has the longest sequence, with a length of " + highestCount);
    }
    return;
  }
}




VB: Private Function hailstone(ByVal n As Long) As Collection
    Dim s As New Collection
    s.Add CStr(n), CStr(n)
    i = 0
    Do While n <> 1
        If n Mod 2 = 0 Then
            n = n / 2
        Else
            n = 3 * n + 1
        End If
        s.Add CStr(n), CStr(n)
    Loop
    Set hailstone = s
End Function
 
Private Function hailstone_count(ByVal n As Long)
    Dim count As Long: count = 1
    Do While n <> 1
        If n Mod 2 = 0 Then
            n = n / 2
        Else
            n = 3 * n + 1
        End If
        count = count + 1
    Loop
    hailstone_count = count
End Function
 
Public Sub rosetta()
    Dim s As Collection, i As Long
    Set s = hailstone(27)
    Dim ls As Integer: ls = s.count
    Debug.Print "hailstone(27) = ";
    For i = 1 To 4
        Debug.Print s(i); ", ";
    Next i
    Debug.Print "... ";
    For i = s.count - 4 To s.count - 1
        Debug.Print s(i); ", ";
    Next i
    Debug.Print s(s.count)
    Debug.Print "length ="; ls
    Dim hmax As Long: hmax = 1
    Dim imax As Long: imax = 1
    Dim count As Integer
    For i = 2 To 100000# - 1
        count = hailstone_count(i)
        If count > hmax Then
            hmax = count
            imax = i
        End If
    Next i
    Debug.Print "The longest hailstone sequence under 100,000 is"; imax; "with"; hmax; "elements."
End Sub