【LeetCode】Validate Binary Search Tree

/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void traverse(TreeNode *root, vector<int> &vals)
    {
        if(NULL==root) return;
        traverse(root->left,vals);
        vals.push_back(root->val);
        traverse(root->right, vals);
    }
    bool isValidBST(TreeNode *root) {
        if(NULL==root) return true;
        vector<int> vals;
        traverse(root, vals);
        for(int i=0;i<vals.size()-1;i++)
            if(vals[i]>=vals[i+1]) return false;
        return true;
    }
};