My feedback/ views on March Challenge 2015 :
Chef and Notebooks :
The easiest of this month’s long challenge, solved it at first attempt. Just went through the question and 5-7 minutes thinking and started coding.
What are those humongous graphs !!! Scared and left it for some later time. After some long thinking I resorted to the old class 11 trigonometry book and found it to be quite a simple problem. Got busy coding and solved it on 15th March, full points in first attempt.
Devu and his Class :
Read it on the first day, seemed to be a problem belonging to easy-medium difficulty, could not solved it. The problem technique seemed somewhat familiar ( now after seeing the editorial I see it is somewhat related to PRLADDU. Didn’t try much as internal/mid semester exam was going on from 04-13 ( bad excuse, others did it, I’m ashamed of my self :’( ).
Count Substrings :
Partially-solved, again seemed easy-medium problem but unfortunately I was unable to pass last three sub-subtask of the last subtask ( task 12, 13, 14 ).
Sereja and Random Array :
At first this problem seemed quite easy, they have already provided the two generator functions with code ( this made me happy, less work in typing and just copy-paste the given functions ). The given generator with some modification and tweaking for faster execution, my solution was accepted with full points.
Started reading and had no idea what to do. finished reading and still no idea what to do !!! Went to the explanation section and saw are those pictures, the problem became more difficult to comprehend. Left it and going through the editorial now.
Chef and Problems :
This problem seemed query based and I thought of implementing segment tree, but again was able to solve it only partially.
Counting on a Tree :
Well I am only a beginner/ advance-beginner and this problem was clearly out of my league.
Random Number Generator :
Seemed quite straight forward and I submitted a brute force approach which gave TLE. Disappointed, I googled around for a few hours for matrix exponentiation and FFT but still TLE, so I left the problem.
I did not try this, just went through it and tried to grasp the approach/logic required to solve it.
What I like about March15 :
A few of the question were based on observations,tricks and mathematics. Ohh I loved the problem “signwave”, so easy but seemed quite hard, requires only +2 level trigonometry ). “Counting on a tree” has a very nice solution ( came to know quite a few things after reading the editorial ). “Sereja and random array” problem was also very nice based on tricks and maths. “Random number generator” involves some nice mathematical theories into a single problem ( great work by the problem author ).
What I dislike about March15 :
Most of the question were based on tricks,mathematics and keen observations. “Matrix” was difficult to grasp, “Random number generator” involves a lot of advanced mathematical manipulation ( Generating functions, FFT, number theoretic transform, polynomial mod, polynomial division, that’s 5 medium/advanced topics into a single problem ).
I agree with @dpraveen , March15 was comparatively tougher than the last few long challenges. Except CNOTE ( and probably SIGNWAVE ) the average difficulty level of the problems were higher compared to other long contests. In the past few long challenges, the difficulty level increased gradually from cakewalk (very easy), easy, easy-medium, medium then medium-difficult, advanced, hard. For three/four problems, some tricks were required. But this month almost all the problems ( except CNOTE ) required some level of observations and tweaks. The difficulty level jumped from cakewalk (CNOTE) to medium ( SIGNWAVE is based on observation, QCHEF ) and then jumped directly to hard category( SEAPROAR, TREECNT2, MATRIX, RNG, EMBED ).
The The best thing about March 15 long challenge is probably the editorials. It has been a while since we had such elaborate, well written, designed with examples editorials for Long contests. Awesome work by the editorialist @kevinsogo .
EDIT 1 : I agree with @lebron, upper bound of difficulty should not be decreased but intermediate difficulty level was quite high in March15 ( most of us are not familiar with ACM ICPC or any other training as mentioned by @lebron ).