# Java Program

1. Nov 30, 2004

How would i write a program in java such that if you input an array, it returns the mode of the array. IF there is more than one mode, return the first mode.
Here is my code so far:

any help is appreciated!

thanks

2. Nov 30, 2004

### gnome

First sort the array.
Then think about it some more.

3. Nov 30, 2004

### Hurkyl

Staff Emeritus
Well, a mode is the element with the greatest frequency, right?

Do you know how to find frequency counts?

Sorting? Bah! I can do it in O(n) time!

4. Nov 30, 2004

### gnome

Really? I didn't know there was any way better than O(nlogn) (using a comparison algorithm).

5. Nov 30, 2004

### Hurkyl

Staff Emeritus
Oh, I mean I can do the problem in O(n) time, I didn't mean I can sort in O(n) time (except in special cases).

PS, courtigrad, don't worry about efficiency. Worry about figuring out a way to do it first, then worry about doing it better if you have time / interest.

6. Nov 30, 2004

Code (Text):

// Program returns the mode of an array. If there is more than one mode
// it returns the first mode.
public class Mode
{
public int Modes(int [] a)  // method for class
{
int i;
int frequency [] = new int[ a.length + 1 ];

for( i = 0; i < a.length; i++)
++frequency[ a[i] ];

}
if( frequency[ a[i] ] > frequency[ a[i + 1] ]
{
return a[i];
}
}

is this right?

7. Nov 30, 2004

### gnome

Do you know that a is an array of integers?

if so, suppose a is an array of 100 integers, the biggest one being 56,789.
What if the biggest one is 2,147,483,647?

Now what?

Last edited: Nov 30, 2004
8. Nov 30, 2004

i would have to sort it from leastest to greatest and then find the frequencies. Then check which one has highest frequency

9. Nov 30, 2004

### gnome

Yes, that's what i was thinking. I don't know how Hurkyl's idea would apply in that kind of situation (i.e. very large integers, strings, or other kinds of non-integer data types).

Were you told what kind of data is in the array?

10. Nov 30, 2004

yes, just integers

maybe i should start like this?

Code (Text):
// Program returns the mode of an array. If there is more than one mode
// it returns the first mode.
public class Mode
{
public void sort()
{
int i;
for( i = 1; i < a.length; i++)
for( i = 0; i < a.length - 1; i++)
if( a[i] > a[ i + 1]
{
hold = a[i];
a[i] = a[i+1];
a[i+1] = hold;
}
}

Last edited: Nov 30, 2004
11. Nov 30, 2004

### gnome

Well, sorting works for any kind of integers, so you know one way to do it. If you want to take it further and you have more information about what's in the array you may be able to come up with a way to do it without sorting. Suppose, for example, that you know that it's only small positive integers. Think about that (I'm not going to give it to you -- that would spoil it).

12. Dec 2, 2004

### The Idiot

I have an idea of how to do it, without sorting, in n time, for any integers, be they small or large. It would take some more advanced things, though...

Edit: It might be worth it, though, since it's supposed to return the first mode if there are duplicates. I'm betting that this array is probably already sorted, though, if I know programming classes, and assuming that this one isn't very advanced.

Last edited: Dec 2, 2004