- (NSMutableArray *)numberOfTasksRunningWithStartArray:(NSArray *)startArray endArray:(NSArray *)endArray query:(NSArray *)queryArray
{
    if (!queryArray) return nil;
    if (!startArray) return nil;
    if (!endArray) return nil;
    if (startArray.count != endArray.count) return nil;

    NSMutableArray *countArray = [NSMutableArray array];
    for (NSNumber *query in queryArray) {
        int count = 0;
        for (int i = 0; i < startArray.count; i ++) {
            NSNumber *start = startArray[i];
            NSNumber *end = endArray[i];
            if ([start intValue] <= [query intValue] && [end intValue] > [query intValue]) {
                count ++;
            }
        }
        [countArray addObject:@(count)];
    }
    return countArray;
}