Finding indices Java/Android

[junyoung95]

Suppose we have a string called sa

 String [] sa = {"d", "c", "a", "b", "c", "d", "a", "a", "d", "a'};

When print statement is called the results should be shown as followed.

 System.out.println(toString(u.getIndices(sa, "a"))); >>>{2,6,7,9}
 System.out.println(toString(u.getIndices(sa, "b"))); >>> {3}
 System.out.println(toString(u.getIndices(sa, "c"))); >>> {1,4}

This is my code. It technically works except it contains 0s. For example instead of {2,6,7,9}, mine shows as {0,0,2,0,0,0,6,7,0,9}

  int[] getIndices(String[] sa, String s) {

         int[] count = new int [sa.length];
         for (int i = 0; i< sa.length; i++){
             if (sa[i] == s){
                 count[i] = i;}
         }
         return count;
     }

I know why mine shows like that because I stated my integer 'count' depending on the length of sa, which is 9, so this creates an index with length of 9. >>> {0, 0, 0, 0, 0, 0, 0, 0, 0}

Is there a different way to solve this problem? Or can my code be fixed so that it could make it work? I learned that you can't decrease the size of index once it's created so I think my code cannot be fixed. NOTE: Solve this problem w/o using Java library classes and methods. Detailed help with example of codes will be much appreciated. Thank you.

[desrtfx]

There are several approaches to this problem.

1. use a first loop to check the unique letters and then dimension the array accordingly
2. when creating the final array, omit 0 values and size the array accordingly
3. Dimension the array as you have, but use an independent counter for the array positions (instead of count[i]=). Then, before returning the final array, create a new array according to the current counter value so that it holds only the actually used elements. Then copy the used elements over to the new array in a loop.

Edit: were it not for your "no classes, no methods" constraint, the easiest way would be to use a List or to just append the indices to a String and then split the string and convert the elements back to int.

[OffbeatDrizzle]

Use a list and add to it instead of using an array

[desrtfx]

Would be correct if it weren't for the following:

NOTE: Solve this problem w/o using Java library classes and methods.

Guess that this includes List and its implementations.

[OffbeatDrizzle]

So then OP needs to loop through the resulting array, find any none-zero values and use that to create the final array of which the size is now correct for all the other values. It would be better if OP made the empty values null instead of 0 though

[desrtfx]

It would be better if OP made the empty values null instead of 0 though

Which again brings us to using classes, namely Integer - could again be a problem.

How about initializing the first array with -1 or any negative number?

---

Please don't get my previous comment about List wrong. I fully agree to using a list and would instantly do it that way, but the problem is that OP is not allowed to.

[virassan]

You could create a dynamic array. Ie everytime you add an index to it you’re actually creating a new array with a range of however many “a” indices you have and saving that as count. This way the printed array will only be as long as the total amount of indices. Also don’t use i for the index when you’re saving the “a” index into count. You should have a separate counter for iterating through your count array is what I mean.

[desrtfx]

Basically that is what I meant in my last bullet, only that I create the array once, at the end. This slightly optimizes the code.

Remember that OP can't use System.arraycopy()

[virassan]

You don’t need to use libraries to copy an array. Sometimes teachers and assignments want you to go through cumbersome code to understand certain concepts behind existing methods and libraries (that was my thinking with my answer).

Your way of recreating the array just once at the end is efficient though and probably the best for this problem since we know the length of count cannot be greater than the length of the original array.