Leetcode:297. Serialize and Deserialize Binary Tree

url https://leetcode.com/problems/serialize-and-deserialize-binary-tree/
本題使用層次遍歷就行了，下面給出代碼

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

        // Encodes a tree to a single string.
        public String serialize(TreeNode root) {
            StringBuilder res= new StringBuilder("");
            if (root==null){
                return "[]";
            }

            Queue<TreeNode> queue = new LinkedList<>();
            queue.add(root);
            res.append(root.val);
            while(!queue.isEmpty()) {
                int size = queue.size();
                for(int i=0;i<size;i++) {
                    TreeNode cur = queue.poll();
                    if (cur.left == null) {
                        res.append(",null");
                    } else {
                        res.append(",").append(cur.left.val);
                        queue.add(cur.left);
                    }
                    if (cur.right == null) {
                        res.append(",null");
                    }else {
                        res.append(",").append(cur.right.val);
                        queue.add(cur.right);
                    }
                }
            }
            return "["+res.toString()+"]";
        }


        // Decodes your encoded data to tree.
        public TreeNode deserialize(String data) {
            if (data==null || "".equals(data)) {
                return null;
            }
            data = data.substring(1,data.length()-1);
            String[] array = data.split(",");
            Queue<TreeNode> queue = new LinkedList<>();
            String val = array[0];
            if (val==null || "".equals(val)){
                return null;
            }
            int index = 0;
            TreeNode root = new TreeNode(Integer.valueOf(val));
            queue.add(root);
            while(!queue.isEmpty()) {
                int size = queue.size();
                for (int i=0;i<size;i++) {
                    TreeNode cur = queue.poll();
                    if (!"null".equals(array[++index])) {
                        cur.left = new TreeNode(Integer.valueOf(array[index]));
                        queue.add(cur.left);
                    }
                    if (!"null".equals(array[++index])) {
                        cur.right = new TreeNode(Integer.valueOf(array[index]));
                        queue.add(cur.right);
                    }
                }
            }
            return root;
        }
    }