[Leetcode]Binary Tree Level Order Traversal II

最新推荐文章于 2021-11-18 16:57:58 发布

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本文介绍了一种针对二叉树进行逆序层次遍历的方法，从叶子节点开始逐层向上遍历，最终得到从底层到顶层的节点值序列。通过实例演示了如何实现此功能，并提供了代码示例。

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Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree {3,9,20,#,#,15,7},

return its bottom-up level order traversal as:

[
  [15,7],
  [9,20],
  [3]
]

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

Binary Tree Level Order Traversal的扩展题~不过这题要求从底层往上层遍历~直接就在结果那儿reverse了一下，在网上找了找，好像也没看到有什么更好的解法~

class Solution:
    # @param root, a tree node
    # @return a list of lists of integers
    def levelOrderBottom(self, root):
        if root is None: return []
        cur, res = [root], []
        while cur:
            next, tmp = [], []
            for node in cur:
                tmp.append(node.val)
                if node.left:
                    next.append(node.left)
                if node.right:
                    next.append(node.right)
            res.append(tmp)
            cur = next
        return res[::-1]