使用hashmap來儲存變數和它對應的值，使用Pattern來匹配{{ var }}模式的字串，個人感覺這道題用正則表示式很簡便。

奉上java滿分程式碼

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main{
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        String[] firstLine = scanner.nextLine().split(" ");
        int n = Integer.parseInt(firstLine[0]);
        int m = Integer.parseInt(firstLine[1]);
        List<String> lines = new ArrayList<>();
        for(int i = 0; i < n; i++){
            lines.add(scanner.nextLine());
        }
        HashMap<String, String> hashMap = new HashMap<>();
        for(int i = 0; i < m; i++){
            String line = scanner.nextLine();
            int index = line.indexOf("\"");
            String key = line.substring(0, index - 1);
            String val = line.substring(index + 1, line.length() - 1);
            hashMap.put(key, val);
        }
        scanner.close();


        Pattern pattern = Pattern.compile("\\{\\{ ([0-9a-zA-z_]+) \\}\\}");
        Matcher matcher;
        for(String line : lines){
            matcher = pattern.matcher(line);
            while (matcher.find()){
                String group = matcher.group(0);
                String key = matcher.group(1);
                if(hashMap.containsKey(key)){
                    line = line.replace(group, hashMap.get(key));
                } else{
                    line = line.replace(group, "");
                }
            }
            System.out.println(line);
        }
    }

}