Initial data commit

Task/Balanced-brackets/Fortran/balanced-brackets.f

@@ -0,0 +1,97 @@
+! $ gfortran -g -O0 -std=f2008 -Wall f.f08 -o f.exe
+! $ ./f
+!  compiles             syntax error
+! :
+! :                     ][
+! :                     ]][[
+! :[[[]]]
+! :                     ][[][]][
+! :                     ][[]]][[[]
+! :                     ]]]][]][[[[[
+! :                     ]]]][][]][[[[[
+! :                     ][[[]]]]][]][[[[
+! :                     [[][]]][]]][[[][[]
+! :                     ]]][[][[[[[[[[]]]]]]
+! :[[][[[][]]][]]
+! :[[[][]][][[[]][]][]]
+
+program balanced_brackets
+  implicit none
+  integer :: N
+  character(len=20) :: brackets, fmt
+  write(6,*)'compiles             syntax error'
+  call random_seed
+  do N=0, 10
+     call generate(N, brackets)
+     if (balanced(brackets)) then
+        fmt = '(a,a20)'
+     else
+        fmt = '(a,21x,a20)'
+     end if
+     write(6,fmt)':',brackets
+  end do
+
+  brackets = '[[][[[][]]][]]'
+  if (balanced(brackets)) then
+     fmt = '(a,a20)'
+  else
+     fmt = '(a,21x,a20)'
+  end if
+  write(6,fmt)':',brackets
+
+  N = 10
+  call generate(N, brackets)
+  do while (.not. balanced(brackets)) ! show a balanced set
+     call generate(N, brackets)
+  end do
+  fmt = '(a,a20)'
+  write(6,fmt)':',brackets
+
+contains
+
+  logical function balanced(s)
+    implicit none
+    character(len=*), intent(in) :: s
+    integer :: i, a, n
+    n = len_trim(s)
+    a = 0
+    balanced = .true.
+    do i=1, n
+       if (s(i:i) == '[') then
+          a = a+1
+       else
+          a = a-1
+       end if
+       balanced = balanced .and. (0 <= a)
+    end do
+  end function balanced
+
+  subroutine generate(N, s)
+    implicit none
+    integer, intent(in) :: N
+    character(len=*), intent(out) :: s
+    integer :: L, R, i
+    real, dimension(2*N) :: harvest
+    character :: c
+    i = 1
+    L = 0
+    R = 0
+    s = ' '
+    call random_number(harvest)
+    do while ((L < N) .and. (R < N))
+       if (harvest(i) < 0.5) then
+          L = L+1
+          s(i:i) = '['
+       else
+          R = R+1
+          s(i:i) = ']'
+       end if
+       i = i+1
+    end do
+    c = merge('[', ']', L < N)
+    do while (i <= 2*N)
+       s(i:i) = c
+       i = i+1
+    end do
+  end subroutine generate
+end program balanced_brackets