Sign in to follow this  
TEUTON

which sorting

Recommended Posts

TEUTON    100
suppose i have an array with elements as 0 and 1 only. What will be the best way(running time) to sort it. I thought about adding all elements and then filling arrays with no of 0's and then 1's. Is there any better method than this??

Share this post


Link to post
Share on other sites
SamLowry    1865
You have a O(n) algorithm, it can't get any better than that in terms of time complexity.

This is how I would do it (assuming C++)

void sort(int* p, int size)
{
int* q = p;

while ( size-- != 0 )
{
if ( !*p++ )
{
*q++ = 0;
}
}

while ( p != q )
{
*q++ = 1;
}
}


Two pointers are kept, one (p) scans over the entire array, and each time it encounters a 0, a 0 is written at *q, and q is moved one position to the right. After p has scanned over the entire array, q is used to change all remaining elements to 1.

Share this post


Link to post
Share on other sites
TEUTON    100
I guess my algorithm requires O(2n) time...isn't it



for(i=0;i<size;i++)
{
num += arr[i];
}


for(i=0;i<size-num;i++)
{
arr[i] =0;
}

for(i=num;i<size;i++)
{
arr[i] =1;
}

[/code]

Share this post


Link to post
Share on other sites
SamLowry    1865
In a way, yes. But as far as I know, people consider O(n) = O(2n).
The algorithm I posted is O(2n) as well.

I wouldn't know which one of our algorithms performs better in practice.

Share this post


Link to post
Share on other sites
Johnn    145
Usually, for profiling to be accurate, you should test with various array's size (and a lot bigger than 10 elements)

- edit

And different array's setup (already sorted, 1-0-1-0-1-0..., random, etc.) to test worse case / best case scenarios!

Share this post


Link to post
Share on other sites
SamLowry    1865
With 10000000 elements, using patterns [1,0,1,0,...], [1,1,1,...,0,0,0,...], [0,0,0,...,1,1,1,...] and [0,0,0,0,...], my version is faster, but not by much. Yours is faster with [1,1,1,1,...].

(Not that this way of benchmarking is in any way accurate...)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this