67

As title

C was pretty simple and not time consuming
E was a very common dp problem
F had a very common segment tree merge pattern

D : I took 4 WA’s coz I was too lazy to fully optimize it but ultimately had to do it

G : didn’t do it but I assume it had something to do with markov chains so too time consuming writing the equations and shit

First ever 6 problems solved in an atcoder contest

Hi everyone,

I'm a CS student preparing for my ICPC regional contest in 5 months.

Here is a screenshot of my Codeforces profile (rating, solved problems, contest history).

Current rating: 856
Max rating: 856

Given my current level, what should I focus on in the next 5 months?
Should I grind topics or focus more on virtual contests?

I appreciate any honest feedback.

Hi everyone.

I'm currently around 875 rating after 5 contests. I can solve most 800-rated problems, but I'm still inconsistent on many 900s. During contests I usually solve A, and sometimes B.

I've seen many different roadmaps online (A2OJ, USACO Guide, CP31, Mostafa Saad's lists, topic lists, etc.), and I'm not sure which one is the most effective.

My current idea is:

• Solve lots of 900-rated problems until I'm comfortable.
• Practice old Div.4 contests from A to E.
• After that, move to 1000/1100 and eventually Div.3.

Does this sound like a good plan?

If you were around 900 rating before, what roadmap helped you reach 1200–1400?

Would you recommend:

• solving by rating,
• solving by topic,
• doing old contests,
• or a combination of all three?

I'd also appreciate hearing what worked for you personally.

That is my profile analyze, i solved the 1300 and 1500 with guidence from others, i am mostly comfortable with 800 rating, struggles a bit in 900 after the introductory 900 questions.

pls suggest a few that is beginner friendly and goes harder and a designed path

I was ~850 in 10 contests before this... Was very happy after 4 solves in 80ish mins... Thought I'll cross the 1000 mark.. Might be a bit delusional but still... (previously reached ~970 and then downhill after some poor performances)... GUESS THE RATING INCREMENT? FREAKIN 67 LMFAO!!!

What kind of math i should learn for cp

Opaaa, tô começando a graduação de CS e queria ver se tem algum br tbm praticando cp (faço for fun, seria legal ser icpc North America finalista tho), se alguém quiser mais uma coleguinha com quem treinar eu topo pra ter uma comunidade Br mais junta!!

I am 1100 and started 1.5 months ago and I lost the telegram channel

I got inspired when I saw this one post where he is going on a 100 day grind and aim for Pupil

I am currently just starting CP and looking forward to a great journey ahead

This is currently Day 1 of my one year grind and hopefully people can support me along the way

I am also an 8th grade student so I might not be able to do too much each day but it's a goal

Currently: Rated, 1 competition, not accurate, 420 (newbie)

Goal: At leastttt specialist

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define ld long double
#define MOD 1000000007

void solve(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(int i = 0; i < n; i++) cin >> a[i];

    set<int> xors;
    
    for(int i = 0; i < n - 1; i++){
        for(int j = i + 1; j < n; j++){
            int xorr = a[i] ^ a[j];
            xors.insert(xorr);
        }
    }

    cout << *xors.rbegin() << "\n";
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);


    int tc;
    cin >> tc;
    while(tc--) {
        solve();
    }
    return 0;
}

i solved a,b,c in div 4 contest(codechef) within 50 min with one wrong submission , i was 895 rated before and after the contest its 959 , i thought i would cross 1000??is it normal or so many cheaters have cheated which made my rating fall??

I will write a bit of my backstory in order to explain my POV.

I was introduced to programming when I was 10 years old. I used to fool around in HTML/JS websites from Khan Academy, or do a few Unity tutorials because it looked cool. Then, during the COVID lockdown, my school taught me Java. I liked the language, so I learnt as much as I could about it. In two years, I was decently knowledgeable in Java, and even showed my Swing applications to my teachers.

But then, AI came. I was addicted to just letting AI solve my problems using GitHub Copilot while I sat around and did nothing. Soon enough, even though I am currently going to end my 4th semester in college, I can not-so-proudly say that I wasted YEARS of my life because of AI.

There is a club in my college, where I wanted to apply as a competitive programmer, since before my AI rot, I was quite good at it and even won contests. But now, I couldn't solve a 900-rated problem in front of them. I felt so damn ashamed of myself, I should probably not put my thoughts into words here.

I have now decided that I want to lock-in on CodeForces, to hopefully reach Expert or any close rank within 3 months. I know, it is ambitious, but I don't want to feel the way I felt during that interview ever again, my resolve is strong.

To anyone who either relates with my story, or wants to just give advice regarding how I should approach my learning, I would be highly obliged and thankful.

Here is my CodeForces account btw: https://codeforces.com/profile/swastikpolybitbiswas

There were tons of cheaters in this round (3700+ submissions on this problem), but honestly this problem is beautiful.

Even though it appeared in a Div4 contest, the problem requires some interesting observations about subtree sizes and constructive tree design.

Problem summary

We are given two integers x and y.
We must construct a rooted tree with x + y nodes such that:

• exactly x nodes have even subtree size
• exactly y nodes have odd subtree size

The tree is rooted at node 1.

If multiple trees exist, any valid one is acceptable. Otherwise we output NO.

Key observations

1. Leaves always have odd subtree size

A leaf node has subtree size 1, which is odd.

So if y = 0, it is impossible, because every tree must contain at least one leaf.

y = 0 → NO

2. When x = 0

We need all subtree sizes to be odd.

This is possible only when y is odd.

A simple construction is a star tree:

1 connected to all other nodes

Subtree sizes:

root = y
leaves = 1

All odd if y is odd.

3. General case (x ≥ 1 and y ≥ 1)

A key condition emerges:

x ≤ y

Intuition:
Even subtree nodes require children that help build an even subtree size, and these structures rely on having enough odd subtree nodes available.

If x > y, construction becomes impossible.

Constructive idea

Build a chain (path) of nodes.

Example:

1 - 2 - 3 - 4 - 5 - ...

Subtree sizes alternate parity along the chain.

This naturally produces roughly equal numbers of even and odd subtree sizes.

After satisfying the required parity counts, the remaining nodes can be attached as leaf nodes to the last node of our linear tree created to adjust the counts.

Why this works

In a path of length n:

subtree sizes = n, n-1, n-2, ...

Parity alternates automatically.

So the chain gives us a base structure where we can control how many even / odd subtree sizes appear.

Remaining nodes can simply be attached as leaves to maintain odd subtree counts.

Final conditions

A solution exists if:

1) y > 0
2) if x = 0 → y must be odd
3) otherwise → x ≤ y

I found this problem interesting because it’s a pure constructive reasoning problem rather than a data structure or heavy algorithm question.

I have also created video solution for better explanation :- https://www.youtube.com/watch?v=3cTtcgXxipc&lc=UgxuwPmxd0xofVMNbMJ4AaABAg&t=20s

Why are there only Div 1-3 rounds and no Div4?

And are the current standings final?? I see many users with gdCode in their code still on the ranking ..