#include "leetcode.h" class Solution { public: bool isValidBST(TreeNode *root) { if (!root) return true; inOrder(root); for (int i = 1; i < tree.size(); i++) if (tree[i] <= tree[i - 1]) return false; return true; } private: vector tree; void inOrder(TreeNode *root) { if (!root) return; inOrder(root->left); tree.push_back(root->val); inOrder(root->right); } };