+ (NSArray *)sortedArrayOfArray:(NSArray *)array
{
    // Merge sort algorithm

    // If number of elements is bigger than 2, split in half and call sorting method recursively
    if ([array count] > 2) {

        int firstHalf = [array count] / 2;

        NSRange range;
        range.location = 0;
        range.length = firstHalf;

        NSArray *firstArray = [array subarrayWithRange:range];
        NSArray *sortedFirstHalf = [MergeSort sortedArrayOfArray:firstArray];

        range.location = firstHalf;
        range.length = [array count] - firstHalf;

        NSArray *secondArray = [array subarrayWithRange:range];
        NSArray *sortedSecondHalf = [MergeSort sortedArrayOfArray:secondArray];

        // merge arrays
        NSMutableArray *sortedArray = [[NSMutableArray alloc] initWithCapacity:array.count];
        int i = 0;
        int j = 0;

        for (int k = 0; k < array.count; k++) {
            if ((i != sortedFirstHalf.count) && (j != sortedSecondHalf.count)) {
                if ([[sortedFirstHalf objectAtIndex:i] intValue] < [[sortedSecondHalf objectAtIndex:j] intValue]) {
                    [sortedArray addObject:[sortedFirstHalf objectAtIndex:i]];
                    if (i < sortedFirstHalf.count) i++;
                } else {
                    [sortedArray addObject:[sortedSecondHalf objectAtIndex:j]];
                    if (j < sortedSecondHalf.count) j++;
                }
            } else if (i == sortedFirstHalf.count) {
                // All objects from first array used. Use only second array
                [sortedArray addObject:[sortedSecondHalf objectAtIndex:j]];
                if (j < sortedSecondHalf.count) j++;
            } else if (j == sortedSecondHalf.count){
                [sortedArray addObject:[sortedFirstHalf objectAtIndex:i]];
                if (i < sortedFirstHalf.count) i++;
            } else {
                // This shouldn't happen
                abort();
            }
        }

        return sortedArray;

    } else if ([array count] == 2) {
        // array of 2 elements
        if (array.count != 2) abort();

        if ([[array objectAtIndex:0] intValue] > [[array objectAtIndex:1] intValue]) {
            // if first number is bigger than second, swap values
            NSMutableArray *sortedArray = [[NSMutableArray alloc] initWithCapacity:2];
            [sortedArray addObject:[array objectAtIndex:1]];
            [sortedArray addObject:[array objectAtIndex:0]];

            return sortedArray;
        } else {
            // if first number is already smaller than (or equal to) second number, return
            return array;
        }
    } else if ([array count] == 1) {
        // Single element, return
        return array;
    }

    return array;
}