I came across this problem in codility, and it seemd a little bit too hard especially with the O(n*logn) time complexity and O(n) space complexity.

This is the problem link https://codility.com/programmers/task/zig_zag_escape/.

Can anybody help with their ideas?

Hello, I'm new to the codeforces platform. I participated in the Codeforces Round #408 (Div. 2) a,d i solved 0 problems (3508 rank), yet i became green (pupil) and i got 1370 as rating. Today i participated in Codeforces Round #409 (rated, Div. 2, based on VK Cup 2017 Round 2) and i solved 2 problems (2088 rank) yet i got negative rating (-65). I'm wondering why?