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1110. Delete Nodes And Return Forest

Difficulty Topics

Description

Given the root of a binary tree, each node in the tree has a distinct value.

After deleting all nodes with a value in to_delete, we are left with a forest (a disjoint union of trees).

Return the roots of the trees in the remaining forest. You may return the result in any order.

 

Example 1:

Input: root = [1,2,3,4,5,6,7], to_delete = [3,5]
Output: [[1,2,null,4],[6],[7]]

Example 2:

Input: root = [1,2,4,null,3], to_delete = [3]
Output: [[1,2,4]]

 

Constraints:

  • The number of nodes in the given tree is at most 1000.
  • Each node has a distinct value between 1 and 1000.
  • to_delete.length <= 1000
  • to_delete contains distinct values between 1 and 1000.

Solution

delete-nodes-and-return-forest.py
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def delNodes(self, root: TreeNode, to_delete: List[int]) -> List[TreeNode]:
        res = []
        delete = set(to_delete)

        def dfs(node, is_root):
            if not node: return None

            to_delete = node.val in delete

            if is_root and not to_delete:
                res.append(node)

            node.left = dfs(node.left, to_delete)
            node.right = dfs(node.right, to_delete)

            return None if to_delete else node

        dfs(root, True)

        return res