Add Solution.py to problems 1110.Delete Nodes And Return Forests

solution/1110.Delete Nodes And Return Forest/Solution.py

@@ -0,0 +1,55 @@
+'''
+https://leetcode.com/problems/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 of trees).
+
+Return the roots of the trees in the remaining forest.  You may return the result in any order.
+
+'''
+# Performance
+'''
+Runtime: 52 ms, faster than 99.34% of Python3 online submissions for Delete Nodes And Return Forest.
+Memory Usage: 12.8 MB, less than 100.00% of Python3 online submissions for Delete Nodes And Return Forest.
+'''
+'''
+n: number of node
+m: number of to_delete
+Runtime: O(n)
+Space: O(log n) or O(m)
+'''
+
+
+class Solution:
+    def delNodes(self, root, to_delete):
+        # Change to set to for better check runtime
+        set_delete = set(to_delete)
+        forests = []
+        # Only add a node in the forest when
+        # 1) Its parent is in set_delete
+        # 2) It's not in set_delete
+        # dfs return False when 1) Node is none and 2) node is in set_delete
+        # When that happen, set the parent link to that node to None
+
+        def dfs(node, is_parent_in_delete):
+            nonlocal set_delete, forests
+            if not node:
+                return False
+            # Still traverse subsequent node but return False
+            if node.val in set_delete:
+                if node.left:
+                    dfs(node.left, True)
+                if node.right:
+                    dfs(node.right, True)
+                return False
+            # Add the current node to the forest
+            if is_parent_in_delete:
+                forests.append(node)
+            # Set the child to none when the child is in set_delete
+            if node.left and not dfs(node.left, False):
+                node.left = None
+            if node.right and not dfs(node.right, False):
+                node.right = None
+            return True
+        dfs(root, True)
+        return forests