二叉树的遍历问题

最新推荐文章于 2025-05-20 16:32:26 发布

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最新推荐文章于 2025-05-20 16:32:26 发布

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分类专栏：剑指offer 文章标签：剑指offer

本文链接：https://blog.youkuaiyun.com/u014568072/article/details/87518881

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本文详细介绍了二叉树的遍历方法，包括先序、中序、后序和层次遍历，每种遍历方式都提供了递归和非递归的实现代码，帮助读者深入理解二叉树的数据结构。

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在刷《剑指offer》的过程中做到关于二叉树的题目，顺便将leetcode上二叉树的遍历相关的代码复习一遍：

先序遍历（递归+非递归）
中序遍历（递归+非递归）
后序遍历（递归+非递归）
层次遍历

二叉树先序遍历

递归

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

class Solution(object):
    def __init__(self):
        self.preorder_list = []
        
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root:
            self.preorder_list.append(root.val)
            self.preorderTraversal(root.left)
            self.preorderTraversal(root.right)
        return self.preorder_list

非递归

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

class Solution(object):
    def preorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        preorder_list = []
        node_list = []
        if root:
            node = root
            while node_list or node:
                while node:
                    preorder_list.append(node.val)
                    node_list.append(node)
                    node = node.left
                node = node_list.pop()
                node = node.right
        return preorder_list

二叉树中序遍历

递归

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

class Solution(object):
    def __init__(self):
        self.inorder_list = []
        
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root:
            self.inorderTraversal(root.left)
            self.inorder_list.append(root.val)
            self.inorderTraversal(root.right)
        return self.inorder_list

非递归

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

class Solution(object):
    def inorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        inorder_list = []
        node_list = []
        node = root
        if node:
            while node_list or node:
                while node:
                    node_list.append(node)
                    node = node.left
                node = node_list.pop()
                inorder_list.append(node.val)
                node = node.right
        return inorder_list

二叉树后序遍历

递归

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

class Solution(object):
    def __init__(self):
        self.postorder = []
        
    def postorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if root:
            self.postorderTraversal(root.left)
            self.postorderTraversal(root.right)
            self.postorder.append(root.val)
        return self.postorder

非递归

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

class Solution(object):
    def postorderTraversal(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        postorder_list = []
        node_list = []
        node_queue = []
        node = root
        if root:
            while node or node_list:
                while node:
                    node_list.append(node)
                    node_queue.append(node)
                    node = node.right
                node = node_list.pop()
                node = node.left
            while node_queue:
                postorder_list.append(node_queue.pop().val)
        return postorder_list

二叉树层次遍历

非递归

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

class Solution(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        level_order = []
        if not root:
            return level_order
        node_queue = [root]
        while node_queue:
            cnt = len(node_queue)
            tmp = []
            while cnt > 0:
                node = node_queue.pop(0)
                tmp.append(node.val)
                if node.left:
                    node_queue.append(node.left)
                if node.right:
                    node_queue.append(node.right)
                cnt -= 1
            level_order.append(tmp)
        return level_order