Leetcode141: 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.

/**
 * 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:
    vector<int> tmp;
    void inorder(TreeNode* Node)
    {
        if(!Node)
            return;
        if(Node->left)
            inorder(Node->left);
        tmp.push_back(Node->val);
        if(Node->right)
            inorder(Node->right);
    }
    bool isValidBST(TreeNode* root) {
        inorder(root);
        for(int i = 1; i < tmp.size(); i++)
        {
            if(tmp[i]<=tmp[i-1])
                return false;
        }
        return true;
    }
};