Data update

Task/Two-bullet-roulette/EasyLang/two-bullet-roulette.easy

@@ -13,7 +13,7 @@ proc load .
    rshift
 .
 proc spin .
-   lim = random 6
+   lim = random 1 6
    for i = 1 to lim - 1 : rshift
 .
 func fire .

Task/Two-bullet-roulette/Fortran/two-bullet-roulette.f

@@ -0,0 +1,102 @@
+program roulette
+  use iso_fortran_env, only: real64
+  implicit none
+
+  integer, parameter :: TRIALS = 50000000
+
+  integer  :: scenario, suicides, trial, fp
+  logical  :: cylinder(0:5), fired1, fired2
+  real(kind=real64) :: pct
+
+  call seed_rng()
+
+  write(*, '(a)') 'Russian Roulette Simulation'
+  write(*, '(a)') repeat('=', 58)
+  write(*, '(a, i0, a)') 'Trials: ', TRIALS, ' per scenario'
+  write(*, '(a)') repeat('-', 58)
+  write(*, '(a40, a8, a10)') 'Scenario', 'Result', 'Theory'
+  write(*, '(a)') repeat('-', 58)
+
+  do scenario = 1, 4
+    suicides = 0
+
+    do trial = 1, TRIALS
+      cylinder = .false.
+      fp = 0
+
+      ! Load first bullet
+      call load(cylinder, fp)
+
+      ! A and B: spin after first bullet
+      if (scenario == 1 .or. scenario == 2) call spin(fp)
+
+      ! Load second bullet
+      call load(cylinder, fp)
+
+      ! Always spin before first shot
+      call spin(fp)
+
+      ! First shot
+      fired1 = cylinder(fp)
+      fp = mod(fp + 1, 6)
+
+      ! A and C: spin after first shot
+      if (scenario == 1 .or. scenario == 3) call spin(fp)
+
+      ! Second shot
+      fired2 = cylinder(fp)
+
+      if (fired1 .or. fired2) suicides = suicides + 1
+    end do
+
+    pct = 100.0_real64 * real(suicides, real64) / real(TRIALS, real64)
+
+    select case (scenario)
+    case (1)
+      write(*, '(a40, f7.3, a, a10)') 'A: spin after bullet 1 and after shot 1', pct, '%', '  55.56%'
+    case (2)
+      write(*, '(a40, f7.3, a, a10)') 'B: spin after bullet 1 only',             pct, '%', '  58.33%'
+    case (3)
+      write(*, '(a40, f7.3, a, a10)') 'C: spin after shot 1 only',               pct, '%', '  55.56%'
+    case (4)
+      write(*, '(a40, f7.3, a, a10)') 'D: no extra spins',                        pct, '%', '  50.00%'
+    end select
+  end do
+
+  write(*, '(a)') repeat('=', 58)
+  write(*, '(a)') 'Highest probability of suicide: B'
+  write(*, '(a)') 'Answer: B -- spin the cylinder after loading bullet 1 only'
+
+contains
+
+  ! Load one bullet: scan clockwise from fp+1 for an empty chamber,
+  ! place bullet there, then advance fp one step clockwise.
+  subroutine load(cyl, fp)
+    logical, intent(inout) :: cyl(0:5)
+    integer, intent(inout) :: fp
+    do while (cyl(mod(fp + 1, 6)))
+      fp = mod(fp + 1, 6)
+    end do
+    cyl(mod(fp + 1, 6)) = .true.
+    fp = mod(fp + 1, 6)
+  end subroutine load
+
+  subroutine spin(fp)
+    integer, intent(out) :: fp
+    real :: r
+    call random_number(r)
+    fp = int(r * 6.0)
+  end subroutine spin
+
+  subroutine seed_rng()
+    integer :: n, clock, i
+    integer, allocatable :: seed(:)
+    call random_seed(size=n)
+    allocate(seed(n))
+    call system_clock(count=clock)
+    seed = clock + 93 * [(i, i = 1, n)]
+    call random_seed(put=seed)
+    deallocate(seed)
+  end subroutine seed_rng
+
+end program roulette