[LeetCode]Serialize and Deserialize Binary Tree

第三次写了，一遍过

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        StringBuffer result = new StringBuffer("");
        if (root == null) {
            return "";
        }
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node == null) {
                result.append("N,");
            } else {
                result.append(String.valueOf(node.val) + ",");
                queue.offer(node.left);
                queue.offer(node.right);
            }
        }
        return String.valueOf(result).substring(0, result.length() - 1);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        int length = data.length();
        if (length == 0) {
            return null;
        }
        String[] strs = data.split(",");
        TreeNode result = new TreeNode(Integer.valueOf(strs[0]));
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(result);
        int index = 1;
        while (index < strs.length) {
            TreeNode node = queue.poll();
            TreeNode left, right;
            if (strs[index].equals("N")) {
                left = null;
            } else {
                left = new TreeNode(Integer.valueOf(strs[index]));
            }
            index ++;
            if (strs[index].equals("N")) {
                right = null;
            } else {
                right = new TreeNode(Integer.valueOf(strs[index]));
            }
            index ++;
            node.left = left;
            node.right = right;
            if (left != null) {
                queue.offer(left);
            }
            if (right != null) {
                queue.offer(right);
            }
        }
        return result;
    }
}