This is the quicksort implementation written in Objective-C.

QuickSort.h

- (NSArray *)quicksort:(NSArray *)array

QuickSort.m

- (NSArray *)quicksort:(NSArray *)array
{
    NSMutableArray *helper = [array mutableCopy];
    [self quicksort:helper from:0 to:array.count-1];
    return helper;
}

- (void)quicksort:(NSMutableArray *)array from:(NSInteger)left to:(NSInteger)right
{
    if(left >= right) return;
    
    NSInteger mid = [self partitionArray:array from:left to:right];
    [self quicksort:array from:left to:mid-1];
    [self quicksort:array from:mid+1 to:right];
}

- (NSInteger)partitionArray:(NSMutableArray *)array from:(NSInteger)left to:(NSInteger)right
{
    if(left + 1 == right) {
        if([array[left] integerValue] > [array[right] integerValue]) {
            NSNumber *tmp = array[left];
            array[left] = array[right];
            array[right] = tmp;
        }
        return left;
    }
    NSNumber *pivot = array[right];
    NSInteger p1 = left;
    for(NSInteger j=left; j<right; j++) {
        if([array[j] integerValue] < [pivot integerValue]) {
            NSNumber *tmp = array[p1];
            array[p1] = array[j];
            array[j] = tmp;
            p1 ++;
        }
    }
    NSNumber *tmp = array[p1];
    array[p1] = array[right];
    array[right] = tmp;
    return p1;
}