add TreeNode

Author: supercoderhawk

Python/common_utils.py

@@ -32,3 +32,10 @@ class Interval:
     def __init__(self, s=0, e=0):
         self.start = s
         self.end = e
+
+
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None