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Lets say I have two arrays of integer and I want to merge them without duplicates.

I know I can add them in Set and then can retrieve them as arraylist.

But without using any built-in function how to do it?

Susanta Adhikary
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    This is more of an algorithm question rather than a java one – fejese Jul 01 '14 at 10:35
  • Since youre using Set and ArrayList you will have to use inbuilt functions for them. – damien hawks Jul 01 '14 at 10:36
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    Create array with the combined size, append the two arrays, sort, iterate over and add each element that's different from the previous to a new array. What have _you_ tried? And really, why would you not want to use the built-in methods? – Anders R. Bystrup Jul 01 '14 at 10:39
  • [how-to-concatenate-two-arrays-in-java](http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java) – Bill Lin Jul 01 '14 at 10:42

3 Answers3

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Depends on how you want to merge them, since an array has an ordering of its elements.

You can just add one after the other (easiest) or "zip" them (one element from A, then one from B, then another from A, etc).

The main problem is that you have to do a check in your new array whether it already contains a value you're trying to add. This is easiest with built-in functions and implementations, like Set. There are Set implementations, like HashSet, which give you constant-time performance for looking up values and inserting them.

I really advise you to just do it the "usual" way and not try and reinvent the wheel.

I find this quite readable:

 static int[] merge(int[] a, int[] b) {
     Set<Integer> set = new HashSet<>(Arrays.asList(a));
     set.addAll(Arrays.asList(b)); // skips duplicate as per Set implementation

     return set.toArray(new int[0]);
 }

This uses both duplication and built-in methods, but it's clear and concise.

Davio
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private Set<Integer> mergeWithoutDuplicates(int[] a, int[] b) {
  Set<Integer> set1= new HashSet<Integer>(a.length+b.length);
  for (int i=0; i<a.length; i++) {
      set1.add(a[i]);
  }
  for (int i=0; i<b.length; i++) {
      set1.add(b[i]);
  }
  return set1;

}

This function should serve your purpose

BiswajitP
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A lot of code but here is a sample..

    try{
        int[] a = {1,2,3,4,5,6,7};
        int[] b = {5,6,7,8,9,10};
        int[] c = new int[a.length+b.length];
        int[] fin = new int[a.length+b.length];
        int i = 0;
        for(int j : fin){
            fin[i++] = -1;
        }
        i = 0;
        for(int j : a){
            c[i++] = j;
        }
        for(int j : b){
            c[i++] = j;
        }
        boolean check = false;
        for(int j = 0,k = 0; j < c.length; j++){
            for(int l : fin){
                if( l == c[j] )
                    check = true;
            }
            if(!check){
                fin[k++] = c[j];
            } else check = false;
        }

    } catch(Exception ex){
        ex.printStackTrace();
    }
myxlptlk
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