Li Kou - binary tree pruning

Two fork tree pruning

Give you the root node of the binary tree  root , In addition, the value of each node of the tree is either 0 , Or 1 .

Return to remove all excluded 1 The original binary tree of the subtree .

node node The subtree of is node Plus all itself node The offspring of .

Example 1：

Input ：root = [1,null,0,0,1]
Output ：[1,null,0,null,1]
explain ：
Only the red nodes meet the conditions “ All do not contain 1 The subtree of ”. On the right is the answer .
Example 2：

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

Input ：root = [1,1,0,1,1,0,1,0]
Output ：[1,1,0,1,1,null,1]

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/binary-tree-pruning
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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    // Subsequent traversal plus recursion 
     public TreeNode pruneTree(TreeNode root) {
        if(root == null) {
            return null;
        }
        root.left = pruneTree(root.left);
        root.right = pruneTree(root.right);
        if(root.left == null && root.right == null && root.val == 0) {
            return null;
        }
        return root;
    }
}