[LeetCode]Binary Tree Pruning

题目描述:

LeetCode 814. Binary Tree Pruning

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.)

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.

题目大意:

给定01二叉树,对二叉树进行剪枝。

剪枝规则为,如果子树中只包含0节点,则移除整棵子树。

解题思路:

递归(Recursion)

Python代码:

# 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 pruneTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        if not root: return root
        root.left = self.pruneTree(root.left)
        root.right = self.pruneTree(root.right)
        return root if root.left or root.right or root.val else None

 

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