1242. Web Crawler Multithreaded
Description
Given a URL startUrl
and an interface HtmlParser
, implement a Multi-threaded web crawler to crawl all links that are under the same hostname as startUrl
.
Return all URLs obtained by your web crawler in any order.
Your crawler should:
- Start from the page:
startUrl
- Call
HtmlParser.getUrls(url)
to get all URLs from a webpage of a given URL. - Do not crawl the same link twice.
- Explore only the links that are under the same hostname as
startUrl
.
![](https://spcdn.pages.dev/leetcode/problems/1242.Web%20Crawler%20Multithreaded/images/urlhostname.png)
As shown in the example URL above, the hostname is example.org
. For simplicity's sake, you may assume all URLs use HTTP protocol without any port specified. For example, the URLs http://leetcode.com/problems
and http://leetcode.com/contest
are under the same hostname, while URLs http://example.org/test
and http://example.com/abc
are not under the same hostname.
The HtmlParser
interface is defined as such:
interface HtmlParser { // Return a list of all urls from a webpage of given url. // This is a blocking call, that means it will do HTTP request and return when this request is finished. public List<String> getUrls(String url); }
Note that getUrls(String url)
simulates performing an HTTP request. You can treat it as a blocking function call that waits for an HTTP request to finish. It is guaranteed that getUrls(String url)
will return the URLs within 15ms. Single-threaded solutions will exceed the time limit so, can your multi-threaded web crawler do better?
Below are two examples explaining the functionality of the problem. For custom testing purposes, you'll have three variables urls
, edges
and startUrl
. Notice that you will only have access to startUrl
in your code, while urls
and edges
are not directly accessible to you in code.
Example 1:
Input: urls = [ "http://news.yahoo.com", "http://news.yahoo.com/news", "http://news.yahoo.com/news/topics/", "http://news.google.com", "http://news.yahoo.com/us" ] edges = [[2,0],[2,1],[3,2],[3,1],[0,4]] startUrl = "http://news.yahoo.com/news/topics/" Output: [ "http://news.yahoo.com", "http://news.yahoo.com/news", "http://news.yahoo.com/news/topics/", "http://news.yahoo.com/us" ]
Example 2:
Input: urls = [ "http://news.yahoo.com", "http://news.yahoo.com/news", "http://news.yahoo.com/news/topics/", "http://news.google.com" ] edges = [[0,2],[2,1],[3,2],[3,1],[3,0]] startUrl = "http://news.google.com" Output: ["http://news.google.com"] Explanation: The startUrl links to all other pages that do not share the same hostname.
Constraints:
1 <= urls.length <= 1000
1 <= urls[i].length <= 300
startUrl
is one of theurls
.- Hostname label must be from
1
to63
characters long, including the dots, may contain only the ASCII letters from'a'
to'z'
, digits from'0'
to'9'
and the hyphen-minus character ('-'
). - The hostname may not start or end with the hyphen-minus character ('-').
- See: https://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_hostnames
- You may assume there're no duplicates in the URL library.
Follow up:
- Assume we have 10,000 nodes and 1 billion URLs to crawl. We will deploy the same software onto each node. The software can know about all the nodes. We have to minimize communication between machines and make sure each node does equal amount of work. How would your web crawler design change?
- What if one node fails or does not work?
- How do you know when the crawler is done?