107. Binary Tree Level Order Traversal II

Difficulty: Easy
34 / 34 test cases passed.
Runtime: 32 ms
Memory Usage: 13.9 MB

Author: YuriSpiridonov

Easy/107.BinaryTreeLevelOrderTraversalII.py

@@ -0,0 +1,51 @@
+"""
+    Given a binary tree, return the bottom-up level order traversal of its 
+    nodes' values. (ie, from left to right, level by level from leaf to root).
+
+    For example:
+    Given binary tree [3,9,20,null,null,15,7],
+            3
+           / \
+          9  20
+            /  \
+           15   7
+    return its bottom-up level order traversal as:
+        [
+          [15,7],
+          [9,20],
+          [3]
+        ]
+"""
+#Difficulty: Easy
+#34 / 34 test cases passed.
+#Runtime: 32 ms
+#Memory Usage: 13.9 MB
+
+#Runtime: 32 ms, faster than 90.65% of Python3 online submissions for Binary Tree Level Order Traversal II.
+#Memory Usage: 13.9 MB, less than 89.09% of Python3 online submissions for Binary Tree Level Order Traversal II.
+
+# 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 levelOrderBottom(self, root: TreeNode) -> List[List[int]]:
+        if not root: return root
+        queue = [root]
+        result = []
+        while queue:
+            length = len(queue)
+            level = []
+            while length:
+                node = queue.pop(0)
+                level.append(node.val)
+                if node.left:
+                    queue.append(node.left)
+                if node.right:
+                    queue.append(node.right)
+                length -= 1    
+            result.append(level)
+        return reversed(result)