added balanced bst

Author: mihirs16

Diff for: 14. Questions/leetcode 110 - balanced bst.py

@@ -0,0 +1,22 @@
+# balanced bst | leetcode 110 | https://leetcode.com/problems/balance-a-binary-search-tree/
+# given a bst, check if it is balanced or not
+# method: for each subtree, check if its left and right subtrees and balanced, and return the maxDepth + 1
+
+# 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:
+    def isBalanced(self, root: Optional[TreeNode]) -> bool:
+        def dfs(root):
+            if root is None: return [True, 0]
+            
+            left, right = dfs(root.left), dfs(root.right)
+            balanced = left[0] and right[0] and abs(left[1] - right[1]) <= 1
+            
+            return [balanced, max(left[1], right[1]) + 1]
+        
+        return dfs(root)[0]