题解 | 序列化与反序列化二叉树

Java层序遍历 使用 # 替代null节点

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
import java.util.*;

public class Solution {
    String Serialize(TreeNode root) {
        LinkedList<TreeNode> queue = new LinkedList<>();
        StringBuffer sb = new StringBuffer();
        if (root == null) {
            sb.append("#");
            return sb.toString();
        }
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node == null) {
                sb.append(",#");
                continue;
            }
            if (sb.length() != 0) sb.append(",");
            sb.append(node.val);
            queue.offer(node.left);
            queue.offer(node.right);
        }
        return sb.toString();
    }
    
    TreeNode Deserialize(String str) {
        String[] items = str.split(",");
        if (items[0].equals("#")) return null;
        LinkedList<TreeNode> queue = new LinkedList<>();
        TreeNode head = new TreeNode(Integer.valueOf(items[0]));
        queue.offer(head);
        int index = 1;
        while (!queue.isEmpty() && index < items.length) {
            TreeNode cur = queue.poll();
            if (!items[index].equals("#")) {
                TreeNode left = new TreeNode(Integer.valueOf(items[index++]));
                cur.left = left;
                queue.offer(left);
            } else {
                cur.left = null;
                index++;
            }
            if (!items[index].equals("#")) {
                TreeNode right = new TreeNode(Integer.valueOf(items[index++]));
                cur.right = right;
                queue.offer(right);
            } else {
                cur.right = null;
                index++;
            }
        }
        return head;
    }
}