$ ./queens -p -n 4
';,a1,a2,a3,a4,
;,b1,b2,b3,b4,
b1:,a3,a4,
b2:,a4,
b3:,a1,
b4:,a1,a2,
;,c1,c2,c3,c4,
c1:,a2,a4,b3,b4,
c2:,a1,a3,b4,
c3:,a2,a4,b1,
c4:,a1,a3,b1,b2,
;,d1,d2,d3,d4,
d1:,a2,a3,b2,b4,c3,c4,
d2:,a1,a3,a4,b1,b3,c4,
d3:,a1,a2,a4,b2,b4,c1,
d4:,a2,a3,b1,b3,c1,c2,
' =~ 
/^;.*,(\w+),.*
;.*,(\w+),.*
[^;]*\2:.*,\1[^;]*
;.*,(\w+),.*
[^;]*\3:.*,\1.*,\2[^;]*
;.*,(\w+),.*
[^;]*\4:.*,\1.*,\2.*,\3[^;]*
/
[a3 b1 c4 d2]
$ ./queens -n 8
[a8 b4 c1 d3 e6 f2 g7 h5]