5 not solved...BST 문제는 GPT 사용

Author: devyulbae

validate-binary-search-tree/devyulbae.py

@@ -1,18 +1,35 @@
 """
 Blind 75 - LeetCode Problem 98: Validate Binary Search Tree
 https://leetcode.com/problems/validate-binary-search-tree/
-이진 탐색 트리인지 확인하기
 
+중위 순회 - 왼쪽 서브트리 -> 루트 -> 오른쪽 서브트리
+중위 순회한 값이 오름차순인지 확인하면 된다.
 """
-from typing import Optional
+from typing import Optional, List
 
 # Definition for a binary tree node.
 class TreeNode:
     def __init__(self, val=0, left=None, right=None):
         self.val = val
         self.left = left
         self.right = right
-        
-class Solution:
+
+class Solution:    # root = [2,1,3] answer = True 
+    def traverse(self, node: Optional[TreeNode], inorder: List[int]) -> None:
+        if not node:
+            return
+        self.traverse(node.left, inorder)
+        inorder.append(node.val)
+        self.traverse(node.right, inorder)
+
+
     def isValidBST(self, root: Optional[TreeNode]) -> bool:
-        
+        inorder = []
+        self.traverse(root, inorder)
+
+        for i in range(1, len(inorder)):
+            if inorder[i] <= inorder[i-1]:
+                return False
+            
+        return True
+