如何从Java中的并行数组中删除重复项？

Question

So, I started learning Java and was wondering how parallel arrays of string and int type could be stored exactly once from the source arrays. For example, I have two arrays parallel to each other, one stores the Phone number as a string and the other stores the duration of the calls as a/an int gotten from each phone number.

String[] phoneNumbers;           
    phoneNumbers = new String[100];
    int[] callDurations = new int[phoneNumbers.length];
    int size = 0;

    phoneNumbers[0] = "888-555-0000";
    callDurations[0] = 10;
    phoneNumbers[1] = "888-555-1234";
    callDurations[1] = 26;
    phoneNumbers[2] = "888-555-0000";
    callDurations[2] = 90;
    phoneNumbers[3] = "888-678-8766";
    callDurations[3] = 28;

    size = 4;

I wrote a method to find the details of a specific phone number, such as the duration of the specific call "888-555-1234" Here is the method and how I called it:

public static void findAllCalls(String[] phoneNumbers, int[] callDurations, int size, String targetNumber) {
    int match;
    System.out.println("Calls from " + targetNumber + ":");
    match = find(phoneNumbers, size, 0, targetNumber);

    while (match >= 0) {
        System.out.println(phoneNumbers[match] + " duration: " + callDurations[match] + "s");

        match = find(phoneNumbers, size, match + 1, targetNumber);

    }
}

System.out.println("\n\nAll calls from number: ");
    findAllCalls(phoneNumbers, callDurations, size, "888-555-1234");

The output of this code is:

All calls from number: 
Calls from 888-555-1234:
888-555-1234 duration: 26s
888-555-1234 duration: 28s

Process finished with exit code 0

Whereas,the output I want to get instead is:

All calls from number: 
Calls from 888-555-1234:
888-555-1234 duration: 54s


Process finished with exit code 0

(26s + 28s)

How is it possible in java to make sure there are no duplicates stored in a parallel array and get total duration for each phone number instead of having them separately in the arrays?

Answer 1

The question was: "How is it possible in java to make sure there are no duplicates stored in a parallel array and get total duration for each phone number instead of having them separately in the arrays?"

The answer is: There is no (inexpensive) way.

Use a hash map instead. Have a look at java.utils.HashMap . A hash map is a concept to store values (of any kind) associated to a specific key. In your case the values would be the durations, the keys would be your phone number. Therefor you should use a String - Integer hash map here.

On insert do the following:

• For each phone number-duration pair do:
  • Is there already an element in the HashMap of the specified key?
  • No -> Add phone number and duration
  • Yes ->
    • Get the duration stored
    • Add the current duration to the stored duration
    • Overwrite the existing item with the new duration calculated

Later you efficiently can perform a lookup.

Answer 2

A Map is an object that maps keys to values

In your case, you want phone numbers (stored in a String ) to correspond to call duration ( int s). Therefore, you'd declare your HashMap as follows ( Note you can't instantiate Map , it is an interface):

Map<String, Integer> callRecords = new HashMap<String, Integer>();

This is a better version because you no longer need to keep track of two different arrays. Now, instead of

phoneNumbers[0] = "888-555-0000";
callDurations[0] = 10;

You can write:

callRecords.put("888-555-0000", 10);

Answer 3

As already stated in the answers before, you can use a map - will avoid duplicates in both phoneNumber and callDuration ( Java code to Prevent duplicate <Key,Value> pairs in HashMap/HashTable ).

Or, if you want to stick with the String implementation, you can change the logic in the findAllCalls() method.

public static void findAllCalls(String[] phoneNumbers, int[] callDurations, int size, String targetNumber) 
{
   int match;
   System.out.println("Calls from " + targetNumber + ":");
   //match = find(phoneNumbers, size, 0, targetNumber);
   int i = 0, duration = 0;
   while (i<size)
    {
        if(phoneNumbers[i].equals(targetNumber))
            duration+=callDurations[i];
        i++;
      //System.out.println(phoneNumbers[match] + " duration: " + callDurations[match] + "s");
      //match = find(phoneNumbers, size, match + 1, targetNumber);
   }
   System.out.println(targetNumber+" duration : "+duration+"s");
}