Project Euler #29

#load "nums.cma";;

open Big_int;;

let rec generate_combinations a1 a2 b1 b2 =
  let rec generate_single_number a b lim =
    if gt_big_int b lim then
      []
    else
      [power_big_int_positive_big_int a b] @ 
      generate_single_number 
        a (succ_big_int b) lim
  in
  if gt_big_int a1 a2 then
    []
  else
    (generate_single_number 
       a1 b1 b2) @ 
    (generate_combinations 
       (succ_big_int a1) a2 b1 b2);;

let rec uniq lst = match lst with
  [] -> []
| hd :: tl when List.exists (fun x -> eq_big_int x hd) tl -> uniq tl
| hd :: tl -> [hd] @ uniq tl;;

let a1 = big_int_of_int 2;;
let a2 = big_int_of_int 100;;
let b1 = big_int_of_int 2;;
let b2 = big_int_of_int 100;;
Printf.printf "%d\n" 
    (List.length 
       (uniq 
   (generate_combinations a1 a2 b1 b2)));;

Quick to come up but not so fast uniq function.