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   "source": [
    "# Merge Sort\n",
    "© 2021, Joe James"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [],
   "source": [
    "import sys\n",
    "\n",
    "def merge_sort(A):\n",
    "    split(A, 0, len(A)-1)\n",
    "    \n",
    "def split(A, first, last):\n",
    "    if first < last:\n",
    "        middle = (first + last)//2\n",
    "        split(A, first, middle)\n",
    "        split(A, middle+1, last)\n",
    "        merge(A, first, middle, last)\n",
    "        \n",
    "def merge(A, first, middle, last):\n",
    "    L = A[first:middle+1]\n",
    "    R = A[middle+1:last+1]\n",
    "    L.append(sys.maxsize)\n",
    "    R.append(sys.maxsize)\n",
    "    l = r = 0\n",
    "    \n",
    "    for a in range (first, last+1):\n",
    "        if L[l] <= R[r]:\n",
    "            A[a] = L[l]\n",
    "            l += 1\n",
    "        else:\n",
    "            A[a] = R[r]\n",
    "            r += 1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Test Function\n",
    "Set a result flag. The j loop is used to perform 1000 test iterations. The next two lines create and shuffle list A of 100 integers. Then A is passed to our sorting function. The sorted result is compared to a sort using Python's sorted function. After 1000 iterations of the test, the result is printed."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Success\n"
     ]
    }
   ],
   "source": [
    "import random\n",
    "\n",
    "def test(func):\n",
    "    result = 'Success'\n",
    "    for j in range(1000):\n",
    "        A = [k for k in range(100)]\n",
    "        random.shuffle(A)\n",
    "        func(A)\n",
    "        if A != sorted(A):\n",
    "            result = 'Failed'\n",
    "    print(result)\n",
    "test(merge_sort)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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