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   "source": [
    "## Number 136"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "[https://leetcode.com/problems/single-number/](https://leetcode.com/problems/single-number/)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "from typing import List\n",
    "\n",
    "class Solution:\n",
    "    def singleNumber(self, nums: List[int]) -> int:\n",
    "        \"\"\"\n",
    "        Implementation 1\n",
    "        \"\"\"\n",
    "        desired_dict = {}\n",
    "        for i in nums:\n",
    "            if i in desired_dict:\n",
    "                desired_dict[i] = desired_dict[i]+1\n",
    "            else:\n",
    "                desired_dict[i] = 1\n",
    "        \n",
    "        return [i for i in desired_dict.keys() if desired_dict[i]==1][0]\n",
    "    \n",
    "    def singleNumber_revised(self, nums: List[int]) -> int:\n",
    "        \"\"\"\n",
    "        Implementation 2\n",
    "        \"\"\"\n",
    "        desired_set = set()\n",
    "        for i in nums:\n",
    "            if i in desired_set:\n",
    "                desired_set.remove(i)\n",
    "            else:\n",
    "                desired_set.add(i)\n",
    "        \n",
    "        return desired_set.pop()\n",
    "\n",
    "a = Solution()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4\n"
     ]
    }
   ],
   "source": [
    "print(a.singleNumber([4,1,2,1,2]))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "4\n"
     ]
    }
   ],
   "source": [
    "print(a.singleNumber_revised([4,1,2,1,2]))"
   ]
  }
 ],
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