Create is_valid_bst.cpp

Author: avidLearnerInProgress

is_valid_bst.cpp

@@ -0,0 +1,28 @@
+/**
+ * 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:
+    //as per my understanding
+    //the minNode and maxNode during traversal must point to the parent of the current node that we are exploring
+    bool isValidBSTHelper(TreeNode *root, TreeNode *min, TreeNode *max) {
+        if(!root) return true;
+        
+        if(min and root->val <= min->val || max and root->val >= max->val) return false;
+        
+        return isValidBSTHelper(root->left, min, root) and isValidBSTHelper(root->right, root, max); 
+    }
+    
+    bool isValidBST(TreeNode* root) {
+       // if(!root) return true;
+        return isValidBSTHelper(root, NULL, NULL);
+    }
+};