Hello, I'm writing regarding task1916. I would love to hear at least some guides what is wrong with my solution. It seems to be working according to requirements but still getting error. I tried to ask on the forum, but even though my answer appears to be identical to those with success, I'm still failing. Not sure if you can see my code thus will paste it below ( actually this is someone else code, but I tried my identical code), contains only the main while loop, but I'm pretty sure that is enough. As I wrote any suggestions which allows me to make even little progress with this problem would be much appreciated :) while ((updatedIndex < linesFromUpdated.size()) && (originalIndex < linesFromOriginal.size())) { String originalLine = linesFromOriginal.get(originalIndex); String updatedLine = linesFromUpdated.get(updatedIndex); if (updatedLine.equals(originalLine)) { lines.add(new LineItem(Type.SAME, updatedLine)); originalIndex++; updatedIndex++; } else if ((originalIndex + 1 < linesFromOriginal.size()) && (updatedLine.equals(linesFromOriginal.get(originalIndex +1)))) { lines.add(new LineItem(Type.REMOVED, originalLine)); originalIndex++; } else { lines.add(new LineItem(Type.ADDED,updatedLine)); updatedIndex++; } } Regards.