leetcode 98 验证二叉搜索树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isValidBST(TreeNode* root) {
        return isBST(root,LONG_MIN, LONG_MAX);
    }
    bool isBST(TreeNode* root ,long long min,long long max)
    {
         if(!root)
        {
            return true;
        }
        if(root->val<=min || root->val>=max)  //注意边界！！ 不能存在等值
        {
            return false;
        }
        return  isBST(root->left,min,root->val) &&  isBST(root->right,root->val,max); 
    }
};