二叉树遍历

最新推荐文章于 2024-10-21 08:57:50 发布

原创最新推荐文章于 2024-10-21 08:57:50 发布 · 86 阅读

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这篇博客介绍了三种二叉树遍历方法：后序遍历、中序遍历和前序遍历。通过递归和栈实现了这些算法，详细展示了每种遍历方式的逻辑。

递归太简单了不写了

后序遍历

#后序遍历
# 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 postorderTraversal(self, root: TreeNode) -> List[int]:
        res=[]
        p=[]
        pre=None
        r=root
        while p or r:
            while r:#找最左子节点并维护栈
                p.append(r)
                r=r.left
            r=p.pop()
            if not r.right or r.right==pre:
                res.append(r.val)
                pre=r
                r=None
            else:
                p.append(r)#当前节点有右节点返回栈
                r=r.right    
        return res

中序遍历

# 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 inorderTraversal(self, root: TreeNode) -> List[int]:
        stack=[]
        res=[]
        while stack or root:
            if root:
                stack.append(root)
                root=root.left
            else:
                root=stack.pop()
                res.append(root.val)
                root=root.right
        return res

前序遍历
用栈

# 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 preorderTraversal(self, root: TreeNode) -> List[int]:
        p=[root]
        res=[]
        while p:
            r=p.pop()
            if r:
                res.append(r.val)
                p.append(r.right)
                p.append(r.left)
        return res