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   "source": [
    "# [27. 移除元素](https://leetcode.cn/problems/remove-element)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 题目描述 \n",
    "\n",
    "给你一个数组 `nums` 和一个值 `val`，你需要 **[原地](https://baike.baidu.com/item/%E5%8E%9F%E5%9C%B0%E7%AE%97%E6%B3%95)** 移除所有数值等于 `val` 的元素。元素的顺序可能发生改变。然后返回 `nums` 中与 `val` 不同的元素的数量。\n",
    "\n",
    "假设 `nums` 中不等于 `val` 的元素数量为 `k`，要通过此题，您需要执行以下操作：\n",
    "\n",
    "-   更改 `nums` 数组，使 `nums` 的前 `k` 个元素包含不等于 `val` 的元素。`nums` 的其余元素和 `nums` 的大小并不重要。\n",
    "-   返回 `k`。\n",
    "\n",
    "**用户评测：**\n",
    "\n",
    "评测机将使用以下代码测试您的解决方案：\n",
    "\n",
    "```txt\n",
    "int[] nums = [...]; // 输入数组\n",
    "int val = ...; // 要移除的值\n",
    "int[] expectedNums = [...]; // 长度正确的预期答案。\n",
    "                            // 它以不等于 val 的值排序。\n",
    "\n",
    "int k = removeElement(nums, val); // 调用你的实现\n",
    "\n",
    "assert k == expectedNums.length;\n",
    "sort(nums, 0, k); // 排序 nums 的前 k 个元素\n",
    "for (int i = 0; i < actualLength; i++) {\n",
    "    assert nums[i] == expectedNums[i];\n",
    "}\n",
    "```\n",
    "\n",
    "如果所有的断言都通过，你的解决方案将会 **通过**。\n",
    "\n",
    "**示例 1：**\n",
    "\n",
    "```txt\n",
    "输入：nums = [3,2,2,3], val = 3\n",
    "输出：2, nums = [2,2,_,_]\n",
    "解释：你的函数函数应该返回 k = 2, 并且 nums 中的前两个元素均为 2。\n",
    "你在返回的 k 个元素之外留下了什么并不重要（因此它们并不计入评测）。\n",
    "```\n",
    "\n",
    "**示例 2：**\n",
    "\n",
    "```txt\n",
    "输入：nums = [0,1,2,2,3,0,4,2], val = 2\n",
    "输出：5, nums = [0,1,4,0,3,_,_,_]\n",
    "解释：你的函数应该返回 k = 5，并且 nums 中的前五个元素为 0,0,1,3,4。\n",
    "注意这五个元素可以任意顺序返回。\n",
    "你在返回的 k 个元素之外留下了什么并不重要（因此它们并不计入评测）。\n",
    "```\n",
    "\n",
    "**提示：**\n",
    "\n",
    "-   `0 <= nums.length <= 100`\n",
    "-   `0 <= nums[i] <= 50`\n",
    "-   `0 <= val <= 100`"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "---\n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 解答"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "    def removeElement(self, nums, val):\n",
    "        \"\"\"\n",
    "        :type nums: List[int]\n",
    "        :type val: int\n",
    "        :rtype: int\n",
    "        \"\"\"\n",
    "        slow_index = 0\n",
    "        for fast_index in range(len(nums)):\n",
    "            if nums[fast_index] != val:\n",
    "                nums[slow_index] = nums[fast_index]\n",
    "                slow_index += 1\n",
    "        return slow_index, nums[:slow_index]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "ac31a7c1",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "原始数组: 3223\n",
      "原始数组长度: 4\n",
      "剔除3后数组: (2, [2, 2])\n"
     ]
    }
   ],
   "source": [
    "solution = Solution()\n",
    "nums = [3,2,2,3]\n",
    "val = 3\n",
    "print('原始数组:',''.join(map(str, nums)))\n",
    "print('原始数组长度:', len(nums))\n",
    "print('剔除3后数组:', solution.removeElement(nums, val)) # Output: 2"
   ]
  }
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