Leetcode 199. Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

You should return [1, 3, 4].

思路: 本题其实和level traversal一个二叉树几乎一样，只不过每层遍历时的顺序注意是从右向左，而且只要输出第一个元素就可以了。
这里使用了queue的灵活性，我们每次从头部pop一个node，但是从尾部将他的left right child push进入queue。例如如下的tree

我们的queue就应该是 [10, 15  5,  18  12  7  2]

 

 1 class Solution:
 2     # @param root, a tree node
 3     # @return a list of integers
 4     def rightSideView(self, root):
 5         ans = []
 6         if root is None:
 7             return ans
 8         queue = [root]
 9         while queue:
10             size = len(queue)
11             for r in range(size):
12                 top = queue.pop(0)
13                 if r == 0:
14                     ans.append(top.val)
15                 if top.right:
16                     queue.append(top.right)
17                 if top.left:
18                     queue.append(top.left)
19         return ans

 

转载于:https://www.cnblogs.com/lettuan/p/6351251.html