MarkdownParse.java

//https://howtodoinjava.com/java/io/java-read-file-to-string-examples/

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Currency;

public class MarkdownParse {

    public static ArrayList<String> getLinks(String markdown) {
        ArrayList<String> toReturn = new ArrayList<>();
        // find the next [, then find the ], then find the (, then read link upto next )
        int currentIndex = 0;
        while(currentIndex <= markdown.length()) {
            
            int openBracket = markdown.indexOf("[", currentIndex);
            int closeBracket = markdown.indexOf("]", openBracket);
            int openParen = markdown.indexOf("(", closeBracket);
            int closeParen = markdown.indexOf(")", openParen);
            //System.out.println("Current index is " + currentIndex);
            currentIndex = closeParen + 1;
            // no infinite loop
            if(openBracket == -1 || closeParen == -1){
                break;
            }
            //empty link 
            else if((openParen + 1) == closeParen){
                currentIndex = closeParen + 1;
                currentIndex++;
                continue;
            }

            // ! in front of bracket or inside link
            else if((markdown.indexOf("!", currentIndex) == openBracket - 1 || markdown.contains("!"))){
                currentIndex = closeParen + 1;
                currentIndex++;
                continue;
            }
            toReturn.add(markdown.substring(openParen + 1, closeParen));
            currentIndex++;
        }
        return toReturn;
    }


    public static void main(String[] args) throws IOException {
        Path fileName = Path.of(args[0]);
        String content = Files.readString(fileName);
        ArrayList<String> links = getLinks(content);
	    System.out.println(links);
    }
}