Create 98. Valid Binary Search Tree.cpp

Author: ZengruiWang

98. Valid Binary Search Tree.cpp

@@ -0,0 +1,20 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    bool isValidBST(TreeNode* root, long min_val, long max_val){
+        if(!root) return true;
+        return min_val < root->val && root->val < max_val && 
+               isValidBST(root->left, min_val, root->val) && isValidBST(root->right, root->val, max_val);
+    }
+    bool isValidBST(TreeNode* root) {
+        return isValidBST(root, LONG_MIN, LONG_MAX);
+    }
+};