1110 Delete Nodes And Return Forest

🔀 Pick One

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:

      1
     / \
   /     \
  2       3
 / \     / \
4   5   6   7

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.
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# 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: Optional[TreeNode], to_delete: List[int]) -> List[TreeNode]:
        to_del = set(to_delete)
        res = []

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

            root_deleted = node.val in to_del
            if is_root and not root_deleted:
                res.append(node)

            node.left = helper(node.left, root_deleted)
            node.right = helper(node.right, root_deleted)
            return None if root_deleted else node

        helper(root, True)
        return res