/// 剑指 Offer 32 - I. 从上到下打印二叉树
/// <https://leetcode.cn/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/>
use std::{cell::RefCell, rc::Rc};
pub struct Solution;
// Definition for a binary tree node.
#[derive(Debug, PartialEq, Eq)]
pub struct TreeNode {
	pub val: i32,
	pub left: Option<Rc<RefCell<TreeNode>>>,
	pub right: Option<Rc<RefCell<TreeNode>>>,
}

#[allow(unused)]
impl TreeNode {
	#[inline]
	pub fn new(val: i32) -> Self {
		TreeNode { val, left: None, right: None }
	}
}

#[allow(unused)]
impl Solution {
	pub fn level_order(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
		let mut res = vec![];
		if root.is_none() {
			return res
		}
		let mut queue = vec![root.unwrap()]; // queue 表示一层的节点
		while !queue.is_empty() {
			let mut tmp = vec![];
			for node in queue {
				let n1 = node.borrow();
				res.push(n1.val);
				if n1.left.is_some() {
					tmp.push(n1.left.clone().unwrap());
				}
				if n1.right.is_some() {
					tmp.push(n1.right.clone().unwrap());
				}
			}
			queue = tmp;
		}
		res
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn test() {
		assert_eq!(Solution::level_order(None), vec![]);
		assert_eq!(Solution::level_order(Some(Rc::new(RefCell::new(TreeNode::new(3)))),), vec![3]);
	}
}