*(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;    }};