python leetcode 814. Binary Tree Pruning

最新推荐文章于 2024-07-18 16:07:51 发布

DreamerLHQ

最新推荐文章于 2024-07-18 16:07:51 发布

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本文介绍了一种针对二叉树的数据结构操作——剪枝算法。该算法通过递归方式去除所有不含数字1的子树，确保最终二叉树中每个节点至少含有一个值为1的子节点。通过几个具体的例子展示了剪枝过程及其结果。

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We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

剪去二叉树中子树不包含‘1’的部分。

Example 1:
Input: [1,null,0,0,1]
Output: [1,null,0,null,1]
 
Explanation: 
Only the red nodes satisfy the property "every subtree not containing a 1".
The diagram on the right represents the answer.

Example 2:
Input: [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]

Example 3:
Input: [1,1,0,1,1,0,1,0]
Output: [1,1,0,1,1,null,1]

Note:

The binary tree will have at most 100 nodes.

The value of each node will only be 0 or 1.

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

class Solution:
def pruneTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""

if not root:
return None
root.left = self.pruneTree(root.left)
root.right = self.pruneTree(root.right)
if not root.left and not root.right and not root.val:
return None
return root