combinations of a set with given number elements

Question

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

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

and i want to have the combinations of 2 elements lik

Answer 1

You can accomplish this using 2 for-loops. 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.

Answer 2

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];
        [combinations addObject:newCombination];
        NSLog(@"added combination %@", newCombination);
    }
}

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