Coinbase Phone Interview

/**
Question Description

Let’s implement an in-memory filesystem with the following interface:

mkdir(path:string)
write_file(path:string, data:string)
read_file(path:string) -> string
The filesystem structure and all data should be stored in the program’s memory.

------------- Clarifications --------------

Path arguments are expected to be well-formed and no validation is required. A well-formed path has a leading slash, and no trailing slash. For example:

/foo/bar
/foo/bar/file.txt
**/

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

/*
mkdir - POST
/mkdir?path=/a
payload {
    path : string
}

writeFile - POST
/writeFile
payload {
    path: "/a"
    data: "Hey Felix"
}


readFile - GET
/readFile?path=/a/text.txt

response 
{
    data: "Hey Felix"
}

*/


public class FileSystem {
    
    Folder root;
    
    public FileSystem(){
        this.root = new Folder("root", new HashMap<>(), new HashMap<>());
    }
    // HashSet<String> directorySet;
    // {"/a", "/a/b", "/a/c", "/a/"}
    class Folder {
        String name;
        Map<String, Folder> children;
        Map<String, String> files; 
        
        public Folder(String name, Map<String, Folder> children, Map<String, String> files) {
            this.name = name;
            this.children = children;
            this.files = files;
        }
    }
    
    // n
    public void makeDirectory(String path) {
        Map<String, Folder> children = root.children;
        String[] levels = path.split("/");
        int n = levels.length;
        for (int i = 0; i < n - 1; i++) {
            if (children.containsKey(levels[i])) {
                // Directory does not exists
                throw new IllegalArgumentException("Directory does not exist: " + levels[i]);
            }
        }
        
        children.put(levels[n-1], new Folder(levels[n-1], new HashMap<>(), new HashMap<>()));
    }
    
    public void writeFile(String path, String data) {
        String[] levels = path.split("/");
        int n = levels.length;
        Folder currentFolder = root;
        for (int i = 0; i < n-1; i++) {
            currentFolder = root.children.get(levels[i]);
        }
        
        String fileName = levels[n-1];
        currentFolder.files.put(fileName, data);
    }
    
    public String readFile(String path) {
        String[] levels = path.split("/");
        int n = levels.length;
        Folder currentFolder = root;
        for (int i = 0; i < n-1; i++) {
            currentFolder = root.children.get(levels[i]);
        }
        
        return currentFolder.files.get(levels[n-1]);
    }
    
    
    public static void main(String args[] ) throws Exception {
        FileSystem fs = new FileSystem();
        fs.makeDirectory("/a");
        fs.makeDirectory("/b");
        // Map<String, Folder> rootChildren = fs.root.children;
        // for (String key : rootChildren.keySet()) {
        //     System.out.println("Printing Child: " + key);
        // }
        fs.writeFile("/a/file.txt", "Hey Felix");
        System.out.println(fs.readFile("/a/file.txt"));
    }
}