leetcode 199. 二叉树的右视图

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题目链接：leetcode

思路：使用广度优先算法找到一层上的所有节点，第一个就是最右边的

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from collections import deque
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def rightSideView(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root:return []
        q = deque()
        q.append(root)
        res = []
        while q:
            n = len(q)
            for i in range(n):
                node = q.popleft()
                if i == 0:res.append(node.val)
                if node.right:q.append(node.right)
                if node.left:q.append(node.left)
        return res