# combinations of a set with given number elements

i have tried to do that but could not figure it out ,

lets say i have a set : `{1,2,3,4,5}`

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• and i want to have the combinations of 2 elements like :

``````{1,2}
{1,3}
{1,4}
{1,5}
{2,3}
{2,4}
{2,5}
{3,4}
{3,5}
{4,5}
``````

how can i implement that in objective-c?

i have checked the algorithms but i could not figure out how can i do that..
here’s the main url that i have checked previously : Algorithm to return all combinations of k elements from n

if anyone could help me with that i will be really happy..

regards.

### 2 Solutions Collect From Internet About “combinations of a set with given number elements”

Just a nested loop to walk over the array’s elements and writing the combinations to a result array should work (this code is tested and works):

``````NSArray *set = [[NSArray alloc] initWithObjects:
[NSNumber numberWithInteger:1],
[NSNumber numberWithInteger:2],
[NSNumber numberWithInteger:3],
[NSNumber numberWithInteger:4],
[NSNumber numberWithInteger:5], nil];

NSMutableArray *combinations = [[NSMutableArray alloc] init];

for (NSInteger i=0; i<[set count]; i++) {
for(NSInteger j=i+1; j<[set count]; j++){
NSArray *newCombination = [[NSArray alloc] initWithObjects:
[set objectAtIndex:i],
[set objectAtIndex:j],
nil];
}
}
``````

At the end of this nested loop, NSMutableArray combinations contains all your combinations.

You can accomplish this using 2 `for-loop`s. In the first loop, you iterate through the elements as `i` and in the second loop from the value `j=i+1` to the end of the count of the number of elements in the set.

It could be something like this:

`````` for (i = 0; i < length_set; i++)
{
for (j = i + 1;length_set; j++)
{
print ("%d%d\n", set[i], set[j]);
}
}
``````

}

NOTE: Its just a pseudocode and i have not checked for syntax, It is just to show the logic.