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leetcode/0107.Binary-Tree-Level-Order-Traversal-II/README.md

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+# [107. Binary Tree Level Order Traversal II](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/)
+
+## 题目
+
+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],
+
+```c
+    3
+   / \
+  9  20
+    /  \
+   15   7
+```
+
+return its bottom-up level order traversal as:
+
+
+```c
+[
+  [15,7],
+  [9,20],
+  [3]
+]
+```
+ 
+
+## 题目大意
+
+按层序从下到上遍历一颗树。
+
+## 解题思路
+
+用一个队列即可实现。
+
+
+