leetcode——98——Validate Binary Search Tree

Given a binary tree, determine if it is a valid binary search tree (BST).

Assume a BST is defined as follows:

• The left subtree of a node contains only nodes with keys less than the node's key.
• The right subtree of a node contains only nodes with keys greater than the node's key.
• Both the left and right subtrees must also be binary search trees.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool isValidBST(TreeNode* root) {        if(root == NULL) return true;          inOrder(root);          for(int i = 1; i< v.size(); i++)              if(v[i] <= v[i-1]) return false;          return true;                }     void inOrder(TreeNode *root){          if(root->left != NULL) inOrder(root->left);          v.push_back(root->val);          if(root->right != NULL) inOrder(root->right);                }private:        vector<int> v;  };