leetcode 102

python

Author: kyle8998

README.md

@@ -73,6 +73,7 @@ Personal Practice Set - Doing One a Day (sometimes) in a Variety of Languages (M
 | 88 | Easy       | [Merge Sorted Array](leetcode/88-Easy-Merge-Sorted-Array/problem.md)                         | [Python](leetcode/88-Easy-Merge-Sorted-Array/answer.py)           |
 | 100| Easy       | [Same Tree](leetcode/100-Easy-Same-Tree/problem.md)                                          | [Python](leetcode/100-Easy-Same-Tree/answer.py)                   |
 | 101| Easy       | [Symmetric Tree](leetcode/101-Easy-Symmetric-Tree/problem.md)                                | [Python](leetcode/101-Easy-Symmetric-Tree/answer.py)              |
+| 102| Medium     | [Binary Tree Level Order Traversal](leetcode/102-Medium-Binary-Tree-Level-Order-Traversal/problem.md) | [Python](leetcode/102-Medium-Binary-Tree-Level-Order-Traversal/answer.py)|
 | 104| Easy       | [Maximum Depth of Binary Tree](leetcode/104-Easy-Maximum-Depth-Of-Binary-Tree/problem.md)    | [Python](leetcode/104-Easy-Maximum-Depth-Of-Binary-Tree/answer.py)|
 | 105| Medium     | [Construct Binary Tree from Preorder and Inorder Traversal](leetcode/105-Medium-Construct-Binary-Tree-From-Preorder-And-Inorder-Traversal/problem.md) | [Python](leetcode/105-Medium-Construct-Binary-Tree-From-Preorder-And-Inorder-Traversal/answer.py)|
 | 106| Medium     | [Construct Binary Tree from Inorder and Postorder Traversal](leetcode/106-Medium-Construct-Binary-Tree-From-Inorder-And-Postorder-Traversal/problem.md) | [Python](leetcode/106-Medium-Construct-Binary-Tree-From-Inorder-And-Postorder-Traversal/answer.py)|

leetcode/102-Medium-Binary-Tree-Level-Order-Traversal/answer.py

@@ -0,0 +1,34 @@
+#!/usr/bin/python3
+
+#------------------------------------------------------------------------------
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def levelOrder(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[List[int]]
+        """
+        if not root:
+            return []
+        stack = [(root, 0)]
+        result = []
+        
+        while stack:
+            (node, level) = stack.pop(0)
+            if level == len(result):
+                result.append([])
+            result[level].append(node.val)
+            if node.left: stack.append((node.left, level+1))
+            if node.right: stack.append((node.right, level+1))
+            
+        return result 
+
+#------------------------------------------------------------------------------
+#Testing

leetcode/102-Medium-Binary-Tree-Level-Order-Traversal/problem.md

@@ -0,0 +1,25 @@
+# Problem 102: Binary Tree Level Order Traversal
+
+#### Difficulty: Medium
+
+#### Problem
+
+Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).
+
+#### Example
+
+<pre>
+Given binary tree [3,9,20,null,null,15,7],
+    3
+   / \
+  9  20
+    /  \
+   15   7
+return its level order traversal as:
+[
+  [3],
+  [9,20],
+  [15,7]
+]
+</pre>
+