leetcode98

class Solution {
public:
    vector<int> V;
    void postTree(TreeNode* node) {
        if (node != NULL) {
            if (node->left != NULL) {
                postTree(node->left);
            }
            V.push_back(node->val);
            if (node->right != NULL) {
                postTree(node->right);
            }
        }
    }
    bool isValidBST(TreeNode* root) {
        postTree(root);
        for (int i = 1; i < V.size(); i++) {
            if (V[i] <= V[i - 1]) {
                return false;
            }
        }
        return true;
    }
};