Top- Based Adaptive Enumeration in Constraint Programming

Algorithm 3

:-lib(ic).

queens(N, Board):-

 length(Board, N),

 Board:: 1..N,

 (fromto(Board, Q1|Cols, Cols, ) do

  (foreach(Q2, Cols), param(Q1), count(Dist,1,_) do

   noattack(Q1, Q2, Dist)

  )

 ),

%call to search predicate

noattack(Q1,Q2,Dist):-

 Q2 #∖= Q1,

 Q2 - Q1 #∖= Dist,

 Q1 - Q2 #∖= Dist.