from a kitty

problem40.ml

@@ -0,0 +1,32 @@
+let int_pow a b = truncate ((float a) ** (float b));;
+
+let digitize number =
+  let rec aux num acc =
+    match num with 
+      | n when n<10 -> (n::acc)
+      | n -> let digit = n mod 10 in
+            aux (n/10) (digit::acc)
+  in 
+    aux number [];;
+
+
+let rec digcount diglst digsum numsum digs acc =
+  let nextnumsum = 9*(int_pow 10 (digs-1)) in
+    match diglst with
+      | [] -> acc
+      | x::xs when ((digsum<x) && (x<(digsum+digs*nextnumsum))) ->
+          let dig = x-digsum in
+          let num = numsum+(dig / digs)+1 in
+          let digno =  dig mod digs in
+            begin
+              match digno with
+                | 0 -> digcount xs digsum numsum digs ((List.nth (digitize num) (digs-1))*acc)
+                | digno -> digcount xs digsum numsum digs ((List.nth (digitize num) (digno-1))*acc)
+            end
+      | x::xs when (x>(digsum+digs*nextnumsum)) ->
+          digcount diglst (digsum+digs*nextnumsum) (numsum+nextnumsum) (digs+1) acc
+      | _ -> failwith "You have failed"
+;;
+
+let solve = digcount [100;1000;10000;100000;1000000] 9 9 2 1;;
+