😅297. Serialize and Deserialize Binary Tree

https://leetcode.com/problems/serialize-and-deserialize-binary-tree/

我居然写出来了，大概就是null用#表示，数字之间用空格隔开，不用区分层次！！

java的queue不能直接存null，所以我hack了一下，话说有split和trim是真的棒

deserialize的时候也要用到queue，大概是pop出来一个然后assign给它两个child，然后指针再一次性往后移动两位

/**
 * 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) {
        if (root == null) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        Queue<TreeNode> queue = new ArrayDeque<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                if (node.val == 10000) {
                    sb.append("# ");
                } else {
                    sb.append(String.valueOf(node.val) + " ");
                    if (node.left == null) {
                        queue.offer(new TreeNode(10000));
                    } else {
                        queue.offer(node.left);
                    }
                    if (node.right == null) {
                        queue.offer(new TreeNode(10000));
                    } else {
                        queue.offer(node.right);
                    }
                }
            }
            // sb.append("* ");
        }
        return sb.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data.equals("")) {
            return null;
        }
        // System.out.println(data);
        TreeNode dummy = new TreeNode(-1);
        String[] tokens = data.trim().split(" ");
        int start = 0; 
        TreeNode root = null;
        Queue<TreeNode> queue = new ArrayDeque<>();
        int i = 0;
        while (i < tokens.length) {
            if (i == 0) {
                root = new TreeNode(Integer.parseInt(tokens[i++]));
                queue.offer(root);
            } else {
                TreeNode parent = queue.poll();
                String tokenLeft = tokens[i];
                String tokenRight = tokens[i+1];
                i += 2;
                if (!tokenLeft.equals("#")) {
                    // System.out.println(token);
                    parent.left = new TreeNode(Integer.parseInt(tokenLeft));
                    queue.offer(parent.left);
                }
                if (!tokenRight.equals("#")) {
                    // System.out.println(token);
                    parent.right = new TreeNode(Integer.parseInt(tokenRight));
                    queue.offer(parent.right);
                }
            }
        }
        return root;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// TreeNode ans = deser.deserialize(ser.serialize(root));