(phixonline)(not pygments)-->
with javascript_semantics
--
-- demo\rosetta\n_queens.exw
-- =========================
--
sequence co, -- columns occupied
-- (ro is implicit)
fd, -- forward diagonals
bd, -- backward diagonals
board
atom count
procedure solve(integer row, integer N, integer show)
for col=1 to N do
if not co[col] then
integer fdi = col+row-1,
bdi = row-col+N
if not fd[fdi]
and not bd[bdi] then
board[row][col] = 'Q'
co[col] = true
fd[fdi] = true
bd[bdi] = true
if row=N then
if show then
puts(1,join(board,"\n")&"\n")
puts(1,repeat('=',N)&"\n")
end if
count += 1
else
solve(row+1,N,show)
end if
board[row][col] = '.'
co[col] = false
fd[fdi] = false
bd[bdi] = false
end if
end if
end for
end procedure
procedure n_queens(integer N=8, integer show=1)
co = repeat(false,N)
fd = repeat(false,N*2-1)
bd = repeat(false,N*2-1)
board = repeat(repeat('.',N),N)
count = 0
solve(1,N,show)
printf(1,"%d queens: %d solutions\n",{N,count})
end procedure
for N=1 to iff(platform()=JS?12:14) do
n_queens(N,N<5)
end for