validate-binary-search-tree solution

Author: sejineer

validate-binary-search-tree/sejineer.py

@@ -0,0 +1,24 @@
+"""
+시간 복잡도: O(N)
+공간 복잡도: O(N)
+"""
+class Solution:
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+        num_list = []
+
+        def dfs(node: TreeNode):
+            if not node:
+                return
+            
+            dfs(node.left)
+            num_list.append(node.val)
+            dfs(node.right)
+        
+        dfs(root)
+
+        mem = num_list[0]
+        for i in range(1, len(num_list)):
+            if mem >= num_list[i]:
+                return False
+            mem = num_list[i]
+        return True