LeetCode in Python 1110. Delete Nodes And Return Forest

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 o

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]]```

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`.
```# 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 delNodes(self, root, to_delete):
"""
:type root: TreeNode
:type to_delete: List[int]
:rtype: List[TreeNode]
"""
res = []
self.helper(root, to_delete, res, True)
return res

def helper(self, root, to_delete, res, is_root):
if not root:
return None
if root.val in to_delete:
self.helper(root.left, to_delete, res, True)
self.helper(root.right, to_delete, res, True)
return None
else:
if is_root:
res.append(root)

root.left = self.helper(root.left, to_delete, res, False)
root.right = self.helper(root.right, to_delete, res, False)
return root

```