Binary tree pruning

/*
 * Given the root of a binary tree, return the same tree where every subtree (of the given tree) not containing a 1 has been removed.
 * A subtree of a node node is node plus every node that is a descendant of node.
 * Example 1:
 * Input: root = [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: 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]
 * Constraints:
 * The number of nodes in the tree is in the range [1, 200].
 * Node.val is either 0 or 1.
 */
use std::rc::Rc;
use std::cell::RefCell;
impl Solution {
  pub fn prune_tree(root: Option<Rc<RefCell<TreeNode>>>) -> Option<Rc<RefCell<TreeNode>>> {
    root.and_then(|node| {
      let left = node.borrow().left.clone();
      let right = node.borrow().right.clone();
      node.borrow_mut().left = Solution::prune_tree(left);
      node.borrow_mut().right = Solution::prune_tree(right);
      if node.borrow().val == 0 && node.borrow().left.is_none() && node.borrow().right.is_none() {
        None
      } else {
        Some(node)
      }
    })
  }
}