func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
     someArray.append(indexPath)
}

for indices in self.someArray {
                if indices == indexPath {
                    cell.button.setImage(UIImage(named: "selected"), forState: UIControlState.Normal)
                } else {
                    cell.button.setImage(UIImage(named: "unselected"), forState: UIControlState.Normal)
                }
            }