{
  "type": "code_options",
  "author": "https://github.com/begeekmyfriend/leetcode",
  "source": "solution.md",
  "exercise_id": "4655300e1df74e79ae306dd06c7c4cbe",
  "keywords": "树,深度优先搜索,二叉搜索树,二叉树",
  "title": "验证二叉搜索树",
  "desc": [
    {
      "content": "\n<div class=\"notranslate\">\n<p>给你一个二叉树的根节点 <code>root</code> ，判断其是否是一个有效的二叉搜索树。</p>",
      "language": "markdown"
    },
    {
      "content": "\n<p><strong>有效</strong> 二叉搜索树定义如下：</p>",
      "language": "markdown"
    },
    {
      "content": "\n<ul>\n<li>节点的左子树只包含<strong> 小于 </strong>当前节点的数。</li>\n<li>节点的右子树只包含 <strong>大于</strong> 当前节点的数。</li>\n<li>所有左子树和右子树自身必须也是二叉搜索树。</li>\n</ul>",
      "language": "markdown"
    },
    {
      "content": "\n<p>&nbsp;</p>",
      "language": "markdown"
    },
    {
      "content": "\n<p><strong>示例 1：</strong></p>\n<img style=\"width: 302px; height: 182px;\" src=\"https://assets.leetcode.com/uploads/2020/12/01/tree1.jpg\" alt=\"\">\n<pre><strong>输入：</strong>root = [2,1,3]\n<strong>输出：</strong>true\n</pre>",
      "language": "markdown"
    },
    {
      "content": "\n<p><strong>示例 2：</strong></p>\n<img style=\"width: 422px; height: 292px;\" src=\"https://assets.leetcode.com/uploads/2020/12/01/tree2.jpg\" alt=\"\">\n<pre><strong>输入：</strong>root = [5,1,4,null,null,3,6]\n<strong>输出：</strong>false\n<strong>解释：</strong>根节点的值是 5 ，但是右子节点的值是 4 。\n</pre>",
      "language": "markdown"
    },
    {
      "content": "\n<p>&nbsp;</p>",
      "language": "markdown"
    },
    {
      "content": "\n<p><strong>提示：</strong></p>",
      "language": "markdown"
    },
    {
      "content": "\n<ul>\n<li>树中节点数目范围在<code>[1, 10<sup>4</sup>]</code> 内</li>\n<li><code>-2<sup>31</sup> &lt;= Node.val &lt;= 2<sup>31</sup> - 1</code></li>\n</ul>\n</div>",
      "language": "markdown"
    }
  ],
  "answer": [
    {
      "content": "",
      "language": "cpp"
    }
  ],
  "prepared": [
    [
      {
        "content": "",
        "language": "cpp"
      }
    ],
    [
      {
        "content": "",
        "language": "cpp"
      }
    ],
    [
      {
        "content": "",
        "language": "cpp"
      }
    ]
  ],
  "template": {
    "content": "#include <bits/stdc++.h>\nusing namespace std;\nstruct TreeNode\n{\n\tint val;\n\tTreeNode *left;\n\tTreeNode *right;\n\tTreeNode() : val(0), left(nullptr), right(nullptr) {}\n\tTreeNode(int x) : val(x), left(nullptr), right(nullptr) {}\n\tTreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}\n};\nclass Solution\n{\npublic:\n\tbool isValidBST(TreeNode *root)\n\t{\n\t\tstack<TreeNode *> stk;\n\t\tint prev = INT_MIN;\n\t\tbool first = true;\n\t\twhile (!stk.empty() || root != nullptr)\n\t\t{\n\t\t\tif (root != nullptr)\n\t\t\t{\n\t\t\t\tstk.push(root);\n\t\t\t\troot = root->left;\n\t\t\t}\n\t\t\telse\n\t\t\t{\n\t\t\t\troot = stk.top();\n\t\t\t\tstk.pop();\n\t\t\t\tif (!first && prev >= root->val)\n\t\t\t\t{\n\t\t\t\t\treturn false;\n\t\t\t\t}\n\t\t\t\tfirst = false;\n\t\t\t\tprev = root->val;\n\t\t\t\troot = root->right;\n\t\t\t}\n\t\t}\n\t\treturn true;\n\t}\n};",
    "language": "cpp"
  },
  "node_id": "dailycode-afe07aa3dd7c45bc9d6ceb91b6349f93",
  "license": "csdn.net",
  "created_at": 1637894158,
  "topic_link": "https://bbs.csdn.net/topics/600469827"
}