What is the best way to remove repeated elements from a array?

Question

I accept a mobile numbers array, and I need to remove repeated numbers in the array. The way I choose is converting the array to a hashset, then convert it back to an array. Is there any better way?

My code is below:

public static void main (String[] args) {

    String[] mobiles = new String[]{"1", "2", "3", "1", "1"};

    Set<String> data = new HashSet<>(Arrays.asList(mobiles));
    String[] result = data.toArray(new String[0]);

    for (String s : result) {
        System.out.println(s);
    }
}

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score 3 · Answer 1 · answered Apr 11 '19 at 05:25

you can use Java8 Streams as well.

public static void main(String []args){
        String[] mobiles = new String[]{"1", "2", "3", "1", "1"};
        String[] result= Arrays.stream(mobiles).distinct().toArray(String[]::new);
        for (String s : result) {
               System.out.println(s);
        }                             
}

score 2 · Answer 2 · answered Apr 11 '19 at 05:40

Simplest way is to use a LinkedHashSet. This way, the order is kept:

String[] nonUnique = new String[] { "1", "2", "5", "2", "3", "1" };
List<String> unique = new ArrayList<>(new LinkedHashSet<>(Arrays.asList(nonUnique)));

Generally, I'd suggest using collections instead of arrays.

score 0 · Answer 3 · answered Apr 11 '19 at 05:25

I rather like your current approach. Off the top of my head, you could try to remove duplicates by first sorting the array, and then walking down the array:

int[] mobiles = new int[] {1, 2, 3, 1, 1};
Arrays.sort(mobiles);
List<Integer> result = new ArrayList<>();

int last = -1;
for (int val : mobiles) {
    if (val != last || result.size() == 0) {
        result.add(val);
        last = val;
    }
}

mobiles = new int[result.size()];
for (int i=0; i < result.size(); ++i) {
    mobiles[i] = result.get(i);
}
System.out.println(Arrays.toString(mobiles));

[1, 2, 3]

This answer assumes that you don't want to retain the original order in the array. Of course, "original" order only makes sense once you define which of the duplicates you want to retain.

The performance bottleneck on the above approach depends on how costly it is to sort the array. Assuming this can be done in O(n*lgn), then this would be the overall performance.

score 0 · Answer 4 · answered Apr 11 '19 at 06:03

0

You can use hashmap also for solving this one. Store all the different elements.

Hashmap<Integer,Integer> hm = new Hashmap<>();

    for(int i=0;i<arr.length;i++)
    {
           hm.add(arr[i],1);

    }
Now print the hashmap.

answered Apr 11 '19 at 06:03

Rohit

1

What is the best way to remove repeated elements from a array?

4 Answers4