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Taylor Venable committed bcb814f

Get a little closer to an answer.

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Files changed (1)

OCaml/Euler023.ml

 
 module Euler023 : sig
   val is_abundant : int -> bool
+  val solution : unit -> int list
 end = struct
   let sum l = List.fold_right (fun (n, m) b -> n + m + b) l 0
   let is_abundant n =
     else
       sum (TaylorNumber.factors n) > n
   let solution () =
-    List.filter (not <<- is_abundant) (TaylorList.iota 1 28123);;
-end
+    let a_list = List.filter (not <<- is_abundant) (TaylorList.iota 1 28123) in
+    let a_nums = Array.make 28124 0 in
+    (* Return true when expressible as sum of abundant numbers. *)
+    let expressible n =
+      let rec check' start =
+        let i = ref start in
+        while !i < Array.length a_nums && a_nums.(!i) != 0 do
+          i := !i + 1
+        done;
+        if !i == Array.length a_nums || n < !i || n > !i then
+          false
+        else
+          if a_nums.(n - !i) == 1 then true else check' (!i + 1)
+      in
+      check' 1
+    in
+    (* Set values in the array according to the list. *)
+    List.iter (fun n -> a_nums.(n) <- 1) a_list;
+    List.filter (not <<- expressible) (TaylorList.iota 1 (2 * 28123))
+end;;
+
+print_string "Solution = ";
+print_int (List.fold_left (+) 0 (Euler023.solution ()))