2018.12.10 LeetCode 107

Scottnan · Scottnan · commit a191dd320cf0 · 2018-12-05T16:10:42.000+08:00
diff --git a/2018.12.10-leetcode107/Despacito.md b/2018.12.10-leetcode107/Despacito.md
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+# LeetCode 107 Binary Tree Level Order Traversal II
+## 1. Description
+
+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]
+]
+```
+
+## 2. Solution
+```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def levelOrderBottom(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[List[int]]
+        """
+        if root == None:
+            return []
+        tmp = [root, '#']
+        level = []
+        result = []
+        while len(tmp) > 1:
+            head = tmp.pop(0)
+            if head != '#':
+                level.append(head.val)
+                if head.left:
+                    tmp.append(head.left)
+                if head.right:
+                    tmp.append(head.right)
+            else:
+                tmp.append('#')
+                result.insert(0, level)
+                level = []
+        result.insert(0, level)
+        return result
+```
