Merge branch 'develop'

1 files changed, 33 insertions, 0 deletions

diff --git a/comparison/SML/nqueen-12.sml b/comparison/SML/nqueen-12.sml
new file mode 100644
index 0000000..9605312
--- /dev/null
+++ b/comparison/SML/nqueen-12.sml
@@ -0,0 +1,33 @@
+fun member x [] = false
+| member x (y::ys) = if x=y then true else (member x ys);
+
+(* check for (0,q) and (k, qpos[col=k]) where k=1... 
+http://www.nct9.ne.jp/m_hiroi/func/haskell06.html
+    0 1 2    --> 
+  *-------------
+ 1| . . . . . .
+ 2| . . . -3. .  5 - 3 = 2
+ 3| . . -2. . .  5 - 2 = 3
+ 4| . -1. . . .  5 - 1 = 4
+ 5| Q . . . . .  Q position is 5  
+ 6| . +1. . . .  5 + 1 = 6
+ 7| . . +2. . .  5 + 2 = 7
+ 8| . . . +3. .  5 + 2 = 8
+  *-------------
+*)
+fun threat k m [] = false
+  | threat k m (x::xs) =
+   if (k = x-m) orelse (k = m-x) then true
+    else (threat (k+1) m xs);
+
+
+fun queen1 0 b n = []
+  | queen1 m b n =
+    if (member m b) orelse (threat 1 m b) then (queen1 (m-1) b n)
+    else if (length b) = (n-1) then [m::b]@(queen1 (m-1) b n)
+         else (queen1 n (m::b) n) @ (queen1 (m-1) b n);
+
+fun queen n = queen1 n [] n;
+
+val n = 12;
+length (queen n);