I have a problem statement as described below: Write a function that takes this input as a parameter and returns a data structure containing the number of

• clicks that were recorded on each domain AND each subdomain under it.
• For example, a click on "mail.yahoo.com" counts toward the totals for "mail.yahoo.com", "yahoo.com", and "com".
• (Subdomains are added to the left of their parent domain. So "mail" and "mail.yahoo" are not valid domains.
• Note that "mobile.sports" appears as a separate domain near the bottom of the input.)

Below is the input data:

 String[] counts = {
                  "900,google.com",
                  "60,mail.yahoo.com",
                  "10,mobile.sports.yahoo.com",
                  "40,sports.yahoo.com",
                  "300,yahoo.com",
                  "10,stackoverflow.com",
                  "20,overflow.com",
                  "5,com.com",
                  "2,en.wikipedia.org",
                  "1,m.wikipedia.org",
                  "1,mobile.sports",
                  "1,google.co.uk"
                };

Below is the expected output:

calculateClicksByDomain(counts) =>
com:                     1345
google.com:              900
stackoverflow.com:       10
overflow.com:            20
yahoo.com:               410
mail.yahoo.com:          60
mobile.sports.yahoo.com: 10
sports.yahoo.com:        50
com.com:                 5
org:                     3
wikipedia.org:           3
en.wikipedia.org:        2
m.wikipedia.org:         1
mobile.sports:           1
sports:                  1
uk:                      1
co.uk:                   1
google.co.uk:            1

I tried to write a solution for above problem statement:

Map<String, Integer> calculateClicksByDomainMap = new HashMap<>();
        for(int i = 0; i < counts.length; i  ) {
            String[] seperateClickCountsAtComma = counts[i].split("\\,");
            for(int j = 0; j < seperateClickCountsAtComma.length; j  = 2) {
                String clickCounts = seperateClickCountsAtComma[j];
                String domain = seperateClickCountsAtComma[j 1];
                calculateClicksByDomainMap.put(domain, Integer.parseInt(clickCounts));
            }
        }
        
        for(Entry<String, Integer> domainCounts : calculateClicksByDomainMap.entrySet()) {
            String domainName = domainCounts.getKey();
            Integer domainCount = domainCounts.getValue();          
            splitStringOnOccurenceOfDot(domainName);
            //System.out.println(domainName   " "   domainCount);
                //String test[] = domainName.split("\\.");
                //System.out.println(test[0]   "======="   test[1]   "-----");
        }


public static String splitStringOnOccurenceOfDot(String domainName) {
        if(!domainName.contains(".")) {
            return domainName;
        }
        String[] subdomain  = domainName.split("\\.");
        domainName = subdomain[1];
        System.out.println(domainName   "===============" );
        return splitStringOnOccurenceOfDot(domainName);
    }

However, I'm not sure how to split the string using recursion. Can anyone help me what is the efficient way to write code in order to get the expected output? I there a way to solve it using recursion? Thank you for your time.

CodePudding user response：

The Map needs to ConcurrentHashMap, so that it allows concurrent updates.

First for loop with nesting can call the recursive method like below, might not need another for loop:

    Map<String, Integer> calculateClicksByDomainMap = new ConcurrentHashMap<>();
    for (final String count : counts) {
      String[] separateClickCountsAtComma = count.split("\\,");
      for (int j = 0; j < separateClickCountsAtComma.length; j  = 2) {
        Integer clickCount = Integer.parseInt(separateClickCountsAtComma[j]);
        String domain = separateClickCountsAtComma[j   1];
        calculateClicksByDomainMap.put(domain, clickCount);
        splitStringOnOccurenceOfDot(domain.substring(domain.indexOf(".") 1), clickCount, calculateClicksByDomainMap);
      }
    }

Rather than returning a value, recursion add/update map itself.

  public static void splitStringOnOccurenceOfDot(String domainName, Integer domainCount, Map<String, Integer> calculateClicksByDomainMap) {
    if(calculateClicksByDomainMap.containsKey(domainName)) {
      
      Integer newCount = calculateClicksByDomainMap.get(domainName)   domainCount;
      calculateClicksByDomainMap.put(domainName, newCount);
    } else {
      calculateClicksByDomainMap.put(domainName, domainCount);
    }
    if(domainName.contains(".")) {
      splitStringOnOccurenceOfDot(domainName.substring(domainName.indexOf(".") 1), domainCount, calculateClicksByDomainMap);
    }
  }