230 Kth Smallest Element in a BST.py

98 Validate Binary Search Tree.py

Author: peihenglyu

230 Kth Smallest Element in a BST.py

@@ -0,0 +1,25 @@
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution(object):
+    def kthSmallest(self, root, k):
+        """
+        :type root: TreeNode
+        :type k: int
+        :rtype: int
+        """
+        inoerder_list = []
+        def inoiterate(root):
+            if not root:
+                return None
+            inoiterate(root.left)
+            inoerder_list.append(root.val)
+            inoiterate(root.right)
+        
+        inoiterate(root)
+
+        return inoerder_list[k-1]

98 Validate Binary Search Tree.py

@@ -0,0 +1,24 @@
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution(object):
+    def isValidBST(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        if not root:
+            return True
+        test_left = True
+        test_right = True
+        if root.left:
+            if root.left.val >= root.val:
+                test_left = False
+        if root.right:
+            if root.right.val <= root.val:
+                test_right = False
+        return self.isValidBST(root.left) and self.isValidBST(root.right) and test_left and test_right