【層次遍歷】序列化、反序列化二叉樹

藉助輔助隊列，層次操作結果做處理

public class Codec {

   String res;

	// 序列化
	public String serialize(TreeNode root) {
		if (root == null) {
			return "[]";
		}

		Queue<TreeNode> queue = new LinkedList<>();
		queue.add(root);
		res = "[" + root.val;
		while (!queue.isEmpty()) {
			TreeNode node = queue.poll();
			if (node.left != null) {
				queue.add(node.left);
				res += "," + node.left.val;
			} else {
				res += ",null";
			}
			if (node.right != null) {
				queue.add(node.right);
				res += "," + node.right.val;
			} else {
				res += ",null";
			}
		}
		res += "]";
		return res;
	}

	// 反序列化.
	public TreeNode deserialize(String data) {
		if (data.length() == 2) {
			return null;
		}
		// 去括號
		data = data.substring(1, data.length() - 1);
		// 逗號分割
		String str[] = data.split(",");
		Queue<TreeNode> queue = new LinkedList<>();
		TreeNode root = new TreeNode(Integer.valueOf(str[0]));
		queue.add(root);
		int i = 1;
		while (!queue.isEmpty()) {
			TreeNode node = queue.poll();
			if (str[i].equals("null")) {
				node.left = null;
			} else {
				node.left = new TreeNode(Integer.valueOf(str[i]));
				queue.add(node.left);
			}
			i++;
			if (str[i].equals("null")) {
				node.right = null;
			} else {
				node.right = new TreeNode(Integer.valueOf(str[i]));
				queue.add(node.right);
			}
			i++;
		}
		return root;
	}
}