[LeetCode] Challenge log 814

Posted on |
814. Binary Tree Pruning

https://leetcode.com/problems/binary-tree-pruning/description/

Another DFS problem.

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.)

1
2
3
4
5
6
7
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.
1
2
3
Example 2:
Input: [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]
1
2
3
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.
Soulution:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
# 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 root is None:
            return None
        l = self.pruneTree(root.left)
        r = self.pruneTree(root.right)
        if root.val == 0 and l is None and r is None:
            return None
        else:
            root.left = l 
            root.right = r
            return root
0%