leetcode 98. 验证二叉搜索树(边界细节处理防止溢出)

class Solution {
public:
   
   bool isValidBST(TreeNode* root) {

		return dfs(root, LONG_MIN, LONG_MAX);
		/*if (root == NULL)return true;
		if (root->left->val >= root->val||root->val >= root->right->val)
		return false;
		return isValidBST(root->left)&&isValidBST(root->right);*/

	}
	bool dfs(TreeNode*root, long mi,long ma) {
		if (!root )return true;
		if (root->val < mi || root->val > ma)return false;
	 
    return dfs(root->left, mi, root->val-1ll) && dfs(root->right, root->val+1ll, ma);//+-1LLlonglong防止数据溢出
	
	} 
};