Initial data commit

Task/Hailstone-sequence/Fortran/hailstone-sequence.f

@@ -0,0 +1,49 @@
+program Hailstone
+  implicit none
+
+  integer :: i, maxn
+  integer :: maxseqlen = 0, seqlen
+  integer, allocatable :: seq(:)
+
+  call hs(27, seqlen)
+  allocate(seq(seqlen))
+  call hs(27, seqlen, seq)
+  write(*,"(a,i0,a)") "Hailstone sequence for 27 has ", seqlen, " elements"
+  write(*,"(a,4(i0,a),3(i0,a),i0)") "Sequence = ", seq(1), ", ", seq(2), ", ", seq(3), ", ", seq(4), " ...., ",  &
+                                     seq(seqlen-3), ", ", seq(seqlen-2), ", ", seq(seqlen-1), ", ", seq(seqlen)
+
+  do i = 1, 99999
+    call hs(i, seqlen)
+    if (seqlen > maxseqlen) then
+      maxseqlen = seqlen
+      maxn = i
+    end if
+  end do
+  write(*,*)
+  write(*,"(a,i0,a,i0,a)") "Longest sequence under 100000 is for ", maxn, " with ", maxseqlen, " elements"
+
+  deallocate(seq)
+
+contains
+
+subroutine hs(number, length, seqArray)
+  integer, intent(in)  :: number
+  integer, intent(out) :: length
+  integer, optional, intent(inout) :: seqArray(:)
+  integer :: n
+
+  n = number
+  length = 1
+  if(present(seqArray)) seqArray(1) = n
+  do while(n /= 1)
+    if(mod(n,2) == 0) then
+      n = n / 2
+    else
+      n = n * 3 + 1
+    end if
+    length = length + 1
+    if(present(seqArray)) seqArray(length) = n
+  end do
+end subroutine
+
+end program