Time for an 2014 update…

Task/N-queens-problem/GAP/n-queens-problem.gap

@@ -0,0 +1,37 @@
+# Quick and dirty solution, checking all permutations without backtracking (thus it's slow)
+IsSafe := function(a)
+    local n, i, j;
+    n := Length(a);
+    for i in [1 .. n - 1] do
+        for j in [i + 1 .. n] do
+            if AbsInt(a[j] - a[i]) = j - i then
+                return false;
+            fi;
+        od;
+    od;
+    return true;
+end;
+
+Queens := function(n)
+    local p, a, v;
+    v := [];
+    for p in SymmetricGroup(n) do
+        a := List([1 .. n], i -> i^p);
+        if IsSafe(a) then
+            Add(v, a);
+        fi;
+    od;
+    return v;
+end;
+
+v := Queens(8);;
+Length(v);
+PrintArray(PermutationMat(PermListList([1 .. 8], v[1]), 8));
+[ [  0,  0,  1,  0,  0,  0,  0,  0 ],
+  [  0,  0,  0,  0,  0,  1,  0,  0 ],
+  [  0,  1,  0,  0,  0,  0,  0,  0 ],
+  [  0,  0,  0,  0,  1,  0,  0,  0 ],
+  [  0,  0,  0,  0,  0,  0,  0,  1 ],
+  [  1,  0,  0,  0,  0,  0,  0,  0 ],
+  [  0,  0,  0,  0,  0,  0,  1,  0 ],
+  [  0,  0,  0,  1,  0,  0,  0,  0 ] ]