Initial commit

Author: phoenixx1

LeetCode/Top_Interview_Questions/Easy_Collection/Trees/Valid Binary Search Tree.cpp

@@ -0,0 +1,31 @@
+/**
+ * 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:
+    int lastVal = INT_MIN;
+    bool isValidBST(TreeNode* root) {
+        if (root == NULL) {
+			return true;
+		}
+		if (!isValidBST(root->left)) {
+			return false;
+		}
+		if (lastVal >= root->val) {
+			return false;
+		}
+		lastVal = root->val;
+		if (!isValidBST(root->right)) {
+			return false;
+		}
+		return true;
+    }
+};