solution for LC-1110-Delete Nodes and Return Forest

leetcode/1110-delete-nodes-and-return-forest.java

@@ -0,0 +1,42 @@
+package leetcode;
+
+import java.util.*;
+class Solution {
+    static class TreeNode {
+        int val;
+        TreeNode left;
+        TreeNode right;
+        TreeNode() {}
+        TreeNode(int val) { this.val = val; }
+        TreeNode(int val, TreeNode left, TreeNode right) {
+            this.val = val;
+            this.left = left;
+            this.right = right;
+        }
+    }
+    TreeNode helper(TreeNode root, HashSet<Integer> set, List<TreeNode> res){
+        if(root == null)
+            return null;
+        root.left = helper(root.left, set, res);
+        root.right = helper(root.right, set, res);
+        if(set.contains(root.val)){
+            if(root.left != null)
+                res.add(root.left);
+            if(root.right != null)
+                res.add(root.right);
+            root = null;
+        }
+        return root;
+    }
+    public List<TreeNode> delNodes(TreeNode root, int[] to_delete) {
+        HashSet<Integer> set = new HashSet<>();
+        for(int i=0; i<to_delete.length; i++){
+            set.add(to_delete[i]);
+        }
+        List<TreeNode> res = new ArrayList<>();
+        TreeNode node = helper(root, set, res);
+        if(node != null)
+            res.add(node);
+        return res;
+    }
+}