leetcode 144. Binary Tree Preorder Traversal（python）

描述

Given the root of a binary tree, return the preorder traversal of its nodes' values.

Example 1:

Input: root = [1,null,2,3]
Output: [1,2,3]

Example 2:

Input: root = []
Output: []

Example 3:

Input: root = [1]
Output: [1]

Example 4:

Input: root = [1,2]
Output: [1,2]

Example 5:

Input: root = [1,null,2]
Output: [1,2]

Note:

The number of nodes in the tree is in the range [0, 100].
-100 <= Node.val <= 100

解析

根据题意，就是前序遍历对二叉树进行遍历。直接使用递归的方法，按照先根后左再右的顺序，将节点的值放入结果列表中。

解答

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        r = []
        def pre(root):
            if not root:
                return 
            r.append(root.val)
            pre(root.left)
            pre(root.right)
        pre(root)
        return r
        	      
		

运行结果

Runtime: 16 ms, faster than 74.54% of Python online submissions for Binary Tree Preorder Traversal.
Memory Usage: 13.6 MB, less than 17.41% of Python online submissions for Binary Tree Preorder Traversal.

原题链接：leetcode.com/problems/bi…

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