Leetcode 814. Binary Tree Pruning

We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

Example 1:
Input: [1,null,0,0,1]
Output: [1,null,0,null,1]
 
Explanation: 
Only the red nodes satisfy the property "every subtree not containing a 1".
The diagram on the right represents the answer.

Example 2:
Input: [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]

Example 3:
Input: [1,1,0,1,1,0,1,0]
Output: [1,1,0,1,1,null,1]

Note:

• The binary tree will have at most 100 nodes.
• The value of each node will only be 0 or 1.

Code (Java):

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/*  * @lc app=leetcode id=814 lang=java  *  * [814] Binary Tree Pruning  */ /**  * Definition for a binary tree node.  * public class TreeNode {  *     int val;  *     TreeNode left;  *     TreeNode right;  *     TreeNode(int x) { val = x; }  * }  */ class Solution {     public TreeNode pruneTree(TreeNode root) {         if (root == null) {             return null;         }           ResultType ans = pruneTreeHelper(root);           return ans.root;     }       private ResultType pruneTreeHelper(TreeNode root) {         if (root == null) {             return new ResultType(null, true);         }           ResultType left = pruneTreeHelper(root.left);         ResultType right = pruneTreeHelper(root.right);           if (left.isZeroTree) {             root.left = null;         }           if (right.isZeroTree) {             root.right = null;         }           boolean isZeroTree = left.isZeroTree && right.isZeroTree && root.val == 0;                   return new ResultType(root, isZeroTree);     } }   class ResultType {     TreeNode root;     boolean isZeroTree;       public ResultType(TreeNode root, boolean isZeroTree) {         this.root = root;         this.isZeroTree = isZeroTree;     } }