[daily training] 814. Binary tree pruning

subject

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]

Tips ：
The number of nodes in the tree is in the range [1, 200] Inside
Node.val by 0 or 1

Code

/** * Definition for a binary tree node. * public 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; * } * } */
class Solution {
    
    //  recursive , Traversing the tree , Edge traversal changes the structure of the tree 
    public TreeNode pruneTree(TreeNode root) {
    
        if( root == null){
    
            return null;
        }
        //  Judge whether the left and right children of the tree are empty , If it doesn't include 1 The subtree of , Also set it to 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;
    }
}