Binary Tree Preorder Traversal

最新推荐文章于 2022-11-29 02:00:43 发布

原创最新推荐文章于 2022-11-29 02:00:43 发布 · 138 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#lintcode #python

python 同时被 2 个专栏收录

60 篇文章

订阅专栏

lintcode

15 篇文章

订阅专栏

本文介绍了一种实现二叉树前序遍历的方法，包括递归和非递归两种方式。递归方法分为分治法和遍历法；非递归方法使用了栈来辅助实现。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

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

Example
Given:

return [1,2,4,5,3].

Python:

    """
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
    self.val = val
    self.left, self.right = None, None
"""


class Solution:
"""
@param root: The root of binary tree.
@return: Preorder in ArrayList which contains node values.
"""
'''
# divide and conquer
def preorderTraversal(self, root):
    result = []
    if root is None:
        return result

    left = self.preorderTraversal(root.left)
    right = self.preorderTraversal(root.right)

    result.append(root.val)
    result.extend(left)
    result.extend(right)
    return result
'''

'''
# Traverse
def preorderTraversal(self, root):
    result = []
    self.helper(root, result)
    return result

def helper(self, root, result):
    if root is None:
        return
    result.append(root.val)
    if root.left:
        self.helper(root.left, result)
    if root.right:
        self.helper(root.right, result)
'''

# non-recursion
def preorderTraversal(self, root):
    if root is None:
        return []
    stack = [root]
    preorder = []
    while stack:
        node = stack.pop()
        preorder.append(node.val)
        if node.right:
            stack.append(node.right)
        if node.left:
            stack.append(node.left)
    return preorder