How to compare the web element list data in selenium webdriver

I have two list . I need to compare these two list and store the unequal list in an list

List flightdetailsR = driver.findElements(By.xpath(".//li[contains(@class , 'clickable flightItem offerPanel returningLi first selected') or contains(@class , 'clickable flightItem offerPanel returningLi') or contains(@class , 'clickable flightItem offerPanel returningLi last') or contains(@class , 'clickable flightItem returningLi')]"));