Validate Binary Search Tree 验证是二叉树否为搜索树

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
private: vector<int> inorder;    
public:
    bool isValidBST(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root==NULL)
        return true;  
        inorder.clear();
        InOrder(root);
        for(int i = 1;i < inorder.size();i++)
        {
            if(inorder[i] <= inorder[i-1])
            return false;
        }
        return true;
    }
    void InOrder(TreeNode *root)
    {
        if(root==NULL)
        return;
        InOrder(root->left);
        inorder.push_back(root->val);
        InOrder(root->right);
    }
};