I got stuck at this problem while trying to learn sweep line technique. I've read the editorial for that problem and got seriously confused at the "y coordinate for a segment" part. Like ... how can we compare the y coordinate when a segment consist of two points ? (Apparently I think it has something to do with sorting points by increasing x coordinate, but can't figure out why ...). Also why do we only check for intersection with the "above" segment in the active set when we first meet the beginning of a segment, but check for both the "above" and "below" when we meet a segment's end ? Please explain all of my question in details if possible.

P/s : Remember that I have 2 questions ...

Edit: There's no respond ... At this point let me ask something straight, and possibly easier : Do you know any red or generally high ranked people that are willing to answer question from a noob like me ? I'm determined to get good at CP, but literally have no mentor or teacher that can go with me a long way. So I asked a friend long ago if he know a good community where people are willing to help me improve. He answered "Codeforces" and ... here I'm am, 3 years later, finally ready to change from a super lazy guy, ADHD and stuff ... to a better version of my self. I went to CF and all the blog I've posted, every characters I've written on CF is just about CP. Sometime I would receive help, but mostly, 80% of the time, it's just downvotes. I know a beginner like me will ask questions that some of you deem stupid, lame, etc... but I know I need to make mistakes to improve. Now I've set for myself a very difficult, rough goal, and time is against me (if I say what the goal is, I know some people will respond with even more negative feedback, but I'll give away a hint : I'm 17 by now). So I changed to a polyphasic sleep schedule recently, sleep for only 3-4 hours a day (yes that's possible), coding for 14-17h, The rest was spend on eating, taking bath, exercise, chores. The unusual time schedule give me more time, but in turn, I have to abandon CF ranked contest, as it always get in the way of one of my sleep phase. But as I study more, there's one clear disadvantage : I have no one to ask. Internet is a rich source of knowledge, but I can't just "figure it out" for every problem I met. I tried : go to CF -> ask a question -> get downvotes -> try even more to "figure it out" -> solve it, but cost too much time. Time is a luxury that I don't have. I know this blog will just earn me even more downvotes, but I don't really mind it. Please, if you know some one who have the patience and ability, along with kindness to answer some of my question, inform me of that person, I promise I will choose the question wisely (Generally I have a about 2 questions a day that are just beyond my ability because of my rapid pace of learning, failing, and trying (well 16h on average a day is a lot of time, I just have to do something with it) but even one answered question a week is already a bless. Most of my question posted on CF have no answer). I will just stay a grey (I've no other choice), but will try to be a student who work both hard and smart, if I ever have a teacher in CP.