python: add problem 109 and unittest

Author: supercoderhawk

Python/sln_101_200/solution_101_110.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 import math
 from typing import List
+from common_utils import ListNode
 
 
 class TreeNode:
@@ -108,6 +109,36 @@ def levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
         :return:
         """
 
+    def sortedListToBST(self, head: ListNode) -> TreeNode:
+        """
+        109
+        :param head:
+        :return:
+        """
+        if not head:
+            return None
+        mid_node = self.get_mid(head)
+        mid = TreeNode(mid_node.val)
+
+        if mid_node == head:
+            return mid
+
+        mid.left = self.sortedListToBST(head)
+        mid.right = self.sortedListToBST(mid_node.next)
+        return mid
+
+    def get_mid(self, head:ListNode):
+        prev_ptr = None
+        slow_node = fast_node = head
+
+        while fast_node and fast_node.next:
+            prev_ptr = slow_node
+            slow_node = slow_node.next
+            fast_node = fast_node.next.next
+        if prev_ptr:
+            prev_ptr.next = None
+        return slow_node
+
     def isBalanced(self, root: TreeNode) -> bool:
         """
         110

Python/sln_101_200/test_solution_101_110.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 from unittest import TestCase
 from sln_101_200.solution_101_110 import Solution_101_110, TreeNode
-from common_utils import build_binary_tree
+from common_utils import build_binary_tree,build_linked_list
 
 
 class TestSolution_101_110(TestCase):
@@ -26,3 +26,7 @@ def test_maxDepth(self):
     def test_zigzagLevelOrder(self):
         tree = build_binary_tree([3, 9, 20, None, None, 15, 7])
         self.assertEqual(self.sln.zigzagLevelOrder(tree), [[3], [20, 9], [15, 7]])
+
+    def test_sortedListToBST(self):
+        head = build_linked_list([-10,-3,0,5,9])
+        root = self.sln.sortedListToBST(head)