feat: adds binary_tree_inorder_traversal exercise

Author: flamiedev

binary_tree_inorder_traversal.py

@@ -0,0 +1,26 @@
+from typing import List, Optional
+
+
+# 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 inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
+        result = []
+
+        def inorder(root):
+            if not root:
+                return []
+
+            inorder(root.left)
+            result.append(root.val)
+            inorder(root.right)
+
+        inorder(root)
+
+        return result