*(leetcode)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.

思路： BST的中序遍历 是递增的！ 这一条就够判断是否为BST

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