{
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    "tags": []
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   "source": [
    "import qualified Data.IntMap.Strict as Map"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "6dd70e30-9203-45a8-957b-a0a8459a3a28",
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    "tags": []
   },
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   "source": [
    "enumerate = zip [0..]\n",
    "\n",
    "twoSum' :: Map.IntMap Int -> [(Int, Int)] -> Int -> [Int]\n",
    "twoSum' hm [] target = []\n",
    "twoSum' hm ((i, n):xs) target =\n",
    "    let remainder = target - n in\n",
    "    let index = Map.lookup remainder hm in\n",
    "    case index of\n",
    "        Nothing -> twoSum' (Map.insert n i hm) xs target\n",
    "        Just k -> [k, i]\n",
    "\n",
    "twoSum :: [Int] -> Int -> [Int]\n",
    "twoSum nums target =\n",
    "    let hm = Map.empty in\n",
    "    let nums' = enumerate nums in\n",
    "    twoSum' hm nums' target"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "0fd587ec-b060-4722-9bbd-d4f6dd83efe2",
   "metadata": {
    "tags": []
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   "source": [
    "-- Open Assistant:\n",
    "-- Define a custom function to check assertions.\n",
    "assert :: Bool -> String -> IO ()\n",
    "assert True  msg = pure ()\n",
    "assert False msg = ioError $ userError msg"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "85cd567a-8124-4a77-8108-0183a9e6b471",
   "metadata": {
    "tags": []
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "\"All Done\""
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "assert (twoSum [3,3] 6 == [0,1]) \"Case 1 Failed\"\n",
    "assert (twoSum [3,2,4] 6 == [1,2]) \"Case 2 Failed\"\n",
    "assert (twoSum [2,7,11,15] 9 == [0,1]) \"Case 3 Failed\"\n",
    "\n",
    "print \"All Done\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "c631b602-1a58-478b-8a73-294f2e34176d",
   "metadata": {},
   "outputs": [],
   "source": []
  }
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