Leetcode 199. Binary Tree Right Side View

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本文介绍了一种通过递归前序遍历的方法来获取二叉树右侧节点值的算法实现。该算法能有效输出从顶部到底部的二叉树右视图，即站在二叉树右侧看到的节点值。

Problem

Given the root of 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.

Algorithm

Recursive. Pre-order traversal of the tree, just update the nodes at each depth.

Code

# 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 rightSideView(self, root: Optional[TreeNode]) -> List[int]:
        ans = []
        def dfs(root, depth):
            if not root:
                return
            if len(ans) <= depth:
                ans.append(root.val)
            else:
                ans[depth] = root.val
            dfs(root.left, depth+1)
            dfs(root.right, depth+1)

        dfs(root, 0)
        return ans