814. 二叉树剪枝

/**
 * 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 {
    public TreeNode pruneTree(TreeNode root) {
        if(containsOne(root))
        {
            return root;
        }
        else
        {
            return null;
        }
        
    }
    public boolean containsOne(TreeNode node)
    {
       if(node == null) return false;

       boolean left = containsOne(node.left);
       boolean right = containsOne(node.right);
       if(left == false)
       {
           node.left =null;
       }
       if(right == false)
       {
           node.right = null;
       }

       return node.val == 1 || left || right;

    }
}