Input data:
[1,3,2,5]
[2,1,3,null,4,null,7]

Actual
  ✔ runtime: 0 ms
  ✘ answer: [3,4,5,5,4,7]
  ✔ stdout: ''

Expected
  ✔ runtime: 0 ms
  ✔ answer: [3,4,5,5,4,null,7]
  ✔ stdout: ''

Input data:
[1,3,2,5]
[2,1,3,null,4,null,7]

Actual
  ✔ runtime: 0 ms
  ✔ answer: [3,4,5,5,4,null,7]
  ✔ stdout: ''

Expected
  ✔ runtime: 0 ms
  ✔ answer: [3,4,5,5,4,null,7]
  ✔ stdout: ''

// 2018-12-26 11:41
// @lc id=617 lang=rust

use std::cell::RefCell;
use std::rc::Rc;
impl Solution {
    pub fn merge_trees(
        t1: Option<Rc<RefCell<TreeNode>>>,
        t2: Option<Rc<RefCell<TreeNode>>>,
    ) -> Option<Rc<RefCell<TreeNode>>> {
        if t1 == None && t2 == None {
            return None;
        }
        let t1_val = {
            if let Some(ref x) = t1 {
                x.clone().borrow().val
            } else {
                0
            }
        };
        let t2_val = {
            if let Some(ref x) = t2 {
                x.clone().borrow().val
            } else {
                0
            }
        };
        let root = Rc::new(RefCell::new(TreeNode::new(t1_val + t2_val)));
        let (t1_left, t1_right) = {
            if let Some(ref x) = t1 {
                (x.borrow().left.clone(), x.borrow().right.clone())
            } else {
                (None, None)
            }
        };

        let (t2_left, t2_right) = {
            if let Some(ref x) = t2 {
                (x.borrow().left.clone(), x.borrow().right.clone())
            } else {
                (None, None)
            }
        };

        root.borrow_mut().left = Solution::merge_trees(t1_left, t2_left);
        root.borrow_mut().right = Solution::merge_trees(t1_right, t2_right);
        return Some(root);
    }
}