8 constant r
create a r 1 + allot

: nqueens
  a r 1 + erase
  0{ s x y t }
  begin
      x 1 + to x
      r a x + c!
      begin
        s 1 + to s
        x to y
        begin y 1 > while
          y 1 - to y
          x a + c@ y a + c@ - to t
          t 0 = x y - t abs = or if
            0 to y
            a x + dup c@ 1 - swap c!
            begin a x + c@ 0 = while
              x 1 - to x
              a x + dup c@ 1 - swap c!
            repeat
          then
        repeat
    y 1 = until
  x r = until
s . ;



8 constant r
create a r 1 + allot
variable s

: nqueens
    0 s ! a r erase
    0
    begin
        1 + r over a + c!
        begin
            s @ 1 + s !
            dup
            begin dup 1 > while
                1 -
                over a + c@ over a + c@ - abs
                dup 0 = 2over - rot = or if
                    drop 0 over a + dup c@ 1 - swap c! swap
                    begin dup a + c@ 0 = while
                        1 - dup a + dup c@ 1 - swap c!
                    repeat
                    swap
                then
            repeat
        1 = until
    dup r = until
    drop
    s @ . ;