I was trying to solve a problem Codeforces Round 291 Div2 B. I have written the following solution with the idea of number of unique slopes being the answer. Please tell what is incorrect with my code. My Code : 166298188 .

Hi, guys. I need some help here. I started doing competitive programming for fun but dropped it . This time I am a bit serious about it and I need your help. I have given a few contests based on my basic programming knowledge.( I don't know any DSA concepts) . I was wondering if some of you would guide me , as to what topics I should cover and in which order. I will collect the resources myself (but if you know some really good resource , then do share) . Just need a little bit of guidance here.