Question

I am using first array to store all database of numbers where some numbers are duplicates.

I have went through this array to see which items are duplicated and am adding index of duplicated items to second array.

Now, I must loop through first array and add all but duplicated values to third array (assuming that we know which fields are duplicated).

But how to do this correctly? I can’t make it stop adding every item from first array to third array.

Assuming I can’t use HashSet().

The purpose of this is to demonstrate how to move one array to other with removed duplicated in O(N) time complexity.

Input numbers: 00, 11, 11, 22, 33, 44, 55, 55, 66, 77, 88, 99
Output which index are duplicated: 1, 2, 6, 7
Output I get: 00, 11, 11, 22, 33, 44, 55, 55, 66, 77, 88, 99 (same as the input)

Code:

   public void dups() 
   {
       int[] b = new int[100];
       int[] c = new int[100];

       int k = 0;
       int n = 0;
       int p = 0;

       for (int i = 0; i < nElems; i++)
           for (int j = 0; j < nElems; j++)
               if(a[j].equals(a[i]) && j != i)
                   b[k++] = i;

       for (int l = 0; l < k; l++)
           System.out.print(b[l] + " ");

       for (int m = 0; m < nElems; m++)
           if (m != b[p + 2])
               c[m] = (Integer) a[n++];

       System.out.print("\n");

       for (int o = 0; o < nElems; o++)
           System.out.print(c[o] + " ");
   }

Answer 1

Instead of marking all duplicates you could mark all that have already been seen earlier.

Instead of:

for (int i = 0; i < nElems; i++)
  for (int j = 0; j < nElems; j++)
    if(a[j].equals(a[i]) && j != i)
      b[k++] = i;

Use something like:

for (int i = 0; i < nElems; i++)
  for (int j = i+1; j < nElems; j++)
    if(a[j].equals(a[i]))
      b[k++] = j;

You should then see:

Output which index are duplicated: 2, 7

Which should be much easier to work with.

Here’s a working solution – although I wouldn’t do it this way:

public class Test {
  Integer[] a = {00, 11, 11, 22, 33, 44, 55, 55, 66, 77, 88, 99};
  int nElems = a.length;

  public void dups() {
    int[] b = new int[100];
    int[] c = new int[100];

    int k = 0;
    int n = 0;
    int p = 0;

    for (int i = 0; i < nElems; i++) {
      for (int j = i + 1; j < nElems; j++) {
        if (a[j].equals(a[i])) {
          b[k++] = j;
        }
      }
    }

    for (int l = 0; l < k; l++) {
      System.out.print(b[l] + " ");
    }
    for (int m = 0; m < nElems; m++) {
      if (m != b[p]) {
        c[n++] = a[m];
      } else {
        p += 1;
      }
    }

    System.out.print("\n");

    for (int o = 0; o < nElems - k; o++) {
      System.out.print(c[o] + " ");
    }
  }

  public static void main(String args[]) {
    new Test().dups();
  }
}

which prints:

2 7 
0 11 22 33 44 55 66 77 88 99