leetcode-114 二叉树展开为链表

最新推荐文章于 2025-12-16 14:17:05 发布

原创最新推荐文章于 2025-12-16 14:17:05 发布 · 196 阅读

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文章标签：

#算法 #dfs #leetcode

本文详细解析了二叉树扁平化的四种不同实现方法，包括使用队列、栈、递归和Morris遍历的方式。每种方法都有其独特的优缺点，适合不同的场景需求。

方法一：

class Solution:
    def flatten(self, root: TreeNode) -> None:
        if not root: 
            return
        queue = []
        def dfs(root):
            if not root:
                return
            queue.append(root)
            dfs(root.left)
            dfs(root.right)
        dfs(root)
        head = queue.pop(0)
        head.left = None
        while queue:
            tmp = queue.pop(0)
            tmp.left = None
            head.right = tmp
            head = tmp

方法二：

class Solution:
    def flatten(self, root: TreeNode) -> None:
        if not root: return
        stack = [root]
        pre = TreeNode(-1)
        while stack:
            tmp = stack.pop()
            pre.left, pre.right = None, tmp
            if tmp.right:
                stack.append(tmp.right)
            if tmp.left:
                stack.append(tmp.left)
            pre = tmp
        return pre

方法三：

class Solution:
    def flatten(self, root: TreeNode) -> None:
        self.pre = None
        def dfs(root):
            if not root:return None
            dfs(root.right)
            dfs(root.left)
            root.left = None
            root.right = self.pre
            self.pre = root
        dfs(root)

方法四：

class Solution:
    def flatten(self, root: TreeNode) -> None:
        def dfs(root):
            if not root:return
            dfs(root.left)
            dfs(root.right)
            if root.left:
                pre = root.left
                while pre.right:
                    pre = pre.right
                pre.right = root.right
                root.right = root.left
                root.left = None
        dfs(root)