From 4689e4e80b479be25f7557d05818f5caa723aafa Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Wed, 5 Feb 2025 18:36:31 -0800
Subject: Initial commit.

---
 .../easy/trees/02_valid_binary_search_tree.cc      | 54 ++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 top-interview-questions/easy/trees/02_valid_binary_search_tree.cc

(limited to 'top-interview-questions/easy/trees/02_valid_binary_search_tree.cc')

diff --git a/top-interview-questions/easy/trees/02_valid_binary_search_tree.cc b/top-interview-questions/easy/trees/02_valid_binary_search_tree.cc
new file mode 100644
index 0000000..a071daf
--- /dev/null
+++ b/top-interview-questions/easy/trees/02_valid_binary_search_tree.cc
@@ -0,0 +1,54 @@
+/**
+ * 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 isValidBSTRec(TreeNode* root, int* min, int* max) {
+        if (root->left && root->right) {
+            int leftMin, leftMax, rightMin, rightMax;
+            if (!isValidBSTRec(root->left,  &leftMin,  &leftMax) ||
+                !isValidBSTRec(root->right, &rightMin, &rightMax)) {
+                return false;
+            }
+            *min = std::min(std::min(leftMin, rightMin), root->val);
+            *max = std::max(std::max(leftMax, rightMax), root->val);
+            return (leftMax < root->val) && (root->val < rightMin);
+        }
+        else if (root->left) {
+            int leftMin, leftMax;
+            if (!isValidBSTRec(root->left, &leftMin, &leftMax)) {
+                return false;
+            }
+            *min = std::min(leftMin, root->val);
+            *max = std::max(leftMax, root->val);
+            return (leftMax < root->val);
+        }
+        else if (root->right) {
+            int rightMin, rightMax;
+            if (!isValidBSTRec(root->right, &rightMin, &rightMax)) {
+                return false;
+            }
+            *min = std::min(rightMin, root->val);
+            *max = std::max(rightMax, root->val);
+            return (root->val < rightMin);
+        }
+        else {
+            *min = *max = root->val;
+            return true;
+        }
+    }
+
+    bool isValidBST(TreeNode* root) {
+        if (!root) return true;
+        int minVal, maxVal;
+        return isValidBSTRec(root, &minVal, &maxVal);
+    }
+};
-- 
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