设计内存文件系统

/*
 * LeetCode Problem 588: Design In-Memory File System
 * 
 * The task is to design a file system that can create directories and files, add content to a file, and read content from a file.
 * The following operations should be supported:
 * - ls(path): List the content in the directory specified by the path. If the path is a file, return the file name only.
 * - mkdir(path): Create a directory at the specified path.
 * - addContentToFile(filePath, content): Add content to the file at the specified path. If the file does not exist, create it.
 * - readContentFromFile(filePath): Return the content of the file at the specified path.
 */
 
import java.util.*;
import java.util.stream.Collectors;
 
public class FileSystem {
    private class Node {
        boolean isFile = false;
        String content = "";
        TreeMap<String, Node> children = new TreeMap<>();
    }
 
    private Node root;
 
    public FileSystem() {
        root = new Node();
    }
 
    public List<String> ls(String path) {
        Node node = root;
        List<String> result = new ArrayList<>();
        if (!path.equals("/")) {
            String[] parts = path.split("/");
            node = Arrays.stream(parts)
                          .skip(1)
                          .reduce(root, (current, part) -> current.children.get(part), (a, b) -> b);
            if (node.isFile) {
                result.add(parts[parts.length - 1]);
                return result;
            }
        }
        result.addAll(node.children.keySet());
        return result;
    }
 
    public void mkdir(String path) {
        Node node = root;
        String[] parts = path.split("/");
        Arrays.stream(parts)
              .skip(1)
              .forEach(part -> node = node.children.computeIfAbsent(part, k -> new Node()));
    }
 
    public void addContentToFile(String filePath, String content) {
        Node node = root;
        String[] parts = filePath.split("/");
        node = Arrays.stream(parts)
                      .skip(1)
                      .limit(parts.length - 2)
                      .reduce(root, (current, part) -> current.children.computeIfAbsent(part, k -> new Node()), (a, b) -> b);
        Node fileNode = node.children.computeIfAbsent(parts[parts.length - 1], k -> new Node());
        fileNode.isFile = true;
        fileNode.content += content;
    }
 
    public String readContentFromFile(String filePath) {
        Node node = root;
        String[] parts = filePath.split("/");
        node = Arrays.stream(parts)
                      .skip(1)
                      .reduce(root, (current, part) -> current.children.get(part), (a, b) -> b);
        return node.content;
    }
}