[loop]
input "How many queens (N>=4)";n
if n < 4 then
 print "Must be greater than 4"
 goto [loop]
end if

dim plot$(100,100)
dim q(n+20)
dim e(n+20)
dim o(n+20)
r=n mod 6
if r<>2 and r<>3 then
  gosub [samp]
  goto [shoBoard]
end if
for i=1 to int(n/2)
  e(i) = 2 * i
next
for i=1 to int((n/2)+.5)
 o(i) = 2 *i-1
next
if r = 2 then gosub [edt2]
if r = 3 then gosub [edt3]
s = 1
for i=1 to n
  if e(i)>0 then
    q(s) = e(i)
    s    = s+1
  end if
next
for i=1 to n
  if o(i) > 0 then
    q(s) = o(i)
    s    = s + 1
  end if
next
' print board
[shoBoard]
cls
for i = 1 to n
  plot$(i,26-q(i)) = "*"
  plot$(i,24-n)    = chr$(96+i)
  plot$(n+1,26-i)  = str$(i)
next i
for ii = 1 to 100
 for jj = 1 to 100
  print left$(plot$(jj,ii)+" ",1);
 next jj
print
next ii
end

' the simple case
[samp]
p = 1
for i = 1 to n
  if i mod 2=0 then
    q(p) = i
    p    = p + 1
  end if
next i
for i = 1 to n
  if i mod 2 then
    q(p) = i
    p    = p + 1
  end if
next
return
' edit list when remainder is 2
[edt2]
for i=1 to n
  if o(i) = 3 then
    o(i) = 1
   else
    if o(i)=1 then o(i) = 3
  end if
  if o(i) = 5 then
    o(i)= o(i) -1
   else
    if o(i) = 0 then
      o(i) = 5
      return
    end if
  end if
next

' edit list when remainder is 3
[edt3]
for i = 1 to n
  if e(i) = 2 then
    e(i)  = e(i)-1
   else
    if e(i) = 0 then
      e(i) = 2
      goto [more]
    end if
  end if
next i
' edit list some more
[more]
for i = 1 to n
  if (o(i)=1 or o(i)=3) then
    o(i) = o(i)-1
   else
    if o(i) = 0 then
      o(i)   = 1
      o(i+1) = 3
      return
    end if
  end if
next