September 2017 Update

Task/Hailstone-sequence/MATLAB/hailstone-sequence-1.m

@@ -1,19 +1,11 @@
-   function x = hailstone(n)
-      % iterative definition
-      global VERBOSE;
-      x = 1;
-      while (1)
-        if VERBOSE,
-          printf('%i ',n);   % print element
-        end;
-
-        if n==1,
-          return;
-        elseif mod(n,2),
-          n = 3*n+1;
-        else
-          n = n/2;
-        end;
-        x = x + 1;
-      end;
-   end;
+function x = hailstone(n)
+  x = n;
+  while n > 1
+       % faster than mod(n, 2)
+    if n ~= floor(n / 2) * 2
+      n = n * 3 + 1;
+    else
+      n = n / 2;
+    end
+    x(end + 1) = n; %#ok
+  end

Task/Hailstone-sequence/MATLAB/hailstone-sequence-2.m

@@ -1,4 +1,2 @@
-  global VERBOSE;
-  VERBOSE = 1;    % display of sequence elements turned on
-  N = hailstone(27);   %display sequence
-  printf('\n\n%i\n',N);  %
+x = hailstone(27);
+fprintf('hailstone(27): %d %d %d %d ... %d %d %d %d\nnumber of elements: %d\n', x(1:4), x(end-3:end), numel(x))

Task/Hailstone-sequence/MATLAB/hailstone-sequence-3.m

@@ -1,8 +1,9 @@
-  global VERBOSE;
-  VERBOSE = 0;    % display of sequence elements turned off
-  N = 100000;
-  M = zeros(N,1);
-  for k=1:N,
-     M(k) = hailstone(k);   %display sequence
-  end;
-  [maxLength, n] = max(M)
+N = 1e5;
+maxLen = 0;
+for k = 1:N
+  kLen = numel(hailstone(k));
+  if kLen > maxLen
+    maxLen = kLen;
+    n = k;
+  end
+end

Task/Hailstone-sequence/MATLAB/hailstone-sequence-4.m

@@ -0,0 +1,18 @@
+function [n, maxLen] = longestHailstone(N)
+  maxLen = 0;
+  for k = 1:N
+    a = k;
+    kLen = 1;
+    while a > 1
+      if a ~= floor(a / 2) * 2
+        a = a * 3 + 1;
+      else
+        a = a / 2;
+      end
+      kLen = kLen + 1;
+    end
+    if kLen > maxLen
+      maxLen = kLen;
+      n = k;
+    end
+  end

Task/Hailstone-sequence/MATLAB/hailstone-sequence-5.m

@@ -0,0 +1,3 @@
+>> [n, maxLen] = longestHailstone(1e5)
+n = 77031
+maxLen = 351

Task/Hailstone-sequence/MATLAB/hailstone-sequence-6.m

@@ -0,0 +1,22 @@
+function [n, maxLen] = longestHailstone(N)
+  lenList(N) = 0;
+  lenList(1) = 1;
+  maxLen = 0;
+  for k = 2:N
+    a = k;
+    kLen = 0;
+    while a >= k
+      if a == floor(a / 2) * 2
+        a = a / 2;
+      else
+        a = a * 3 + 1;
+      end
+      kLen = kLen + 1;
+    end
+    kLen = kLen + lenList(a);
+    lenList(k) = kLen;
+    if kLen > maxLen
+      maxLen = kLen;
+      n = k;
+    end
+  end

Task/Hailstone-sequence/MATLAB/hailstone-sequence-7.m

@@ -0,0 +1,3 @@
+>> [n, maxLen] = longestHailstone(1e5)
+n = 77031
+maxLen = 351