Recently, I started solving codeforces problems from the beginning. I just solved Codeforces Beta Round 8. I couldn't find any tutorial for the round so I decided to write tutorial for the last two problems. The others I solve long time ago in the real contest. Problem E took me quite some time and I couldn't find even a discussion about it, so here are my solutions.

D. 8D - Two Friends

The main observation for this problem is the following: If Alan and/or Bob is at some point X and moves following some curve and travels distance d, then the point at which they finish can be ANY point on or inside the circle with center X and radius d. In other words: If you start at some point X and go to some point Y, you can do this on as long curve as we want(only not shorter then the distance(X, Y).

All of us use epsilons in their codes for problems dealing with floating point numbers. Do you have some method of choosing what the value of epsilon to use or use some fixed number. I just solve an old geometry problem: 8D - Two Friends and when I used eps = 1e-9 I failed systests, but when I made eps = 1e-10 my solution passed. This is not the first time I fail because of choosing inappropriate value of eps and I was wondering if you guys use some methods of choosing the value.

PS: In this problem I mainly use epsilon to write a < b + esp instead of a <= b.

• Problems
• Final Standings
• Winner: dzhulgakov