update cf-702C

[freakin23]

Place an "x" in the corresponding checkbox if it is done or does not apply to this pull request.

• I have tested my code.
• I have added my solution according to the steps here.
• I have followed the code conventions mentioned here.
  • I understand that if it is clear that I have not attempted to follow these conventions, my PR will be closed.
  • If changes are requested, I will re-request a review after addressing them.
• I have linked this PR to any issues that it closes.

AC: https://codeforces.com/contest/702/submission/292572139

[freakin23]

Personally, I don't think Solution 3 is needed at all. The towers are already given in sorted order, so there is no point in using a set for that. It just looks like a heavy version of Solution 1.