i am so excited it is my first *out of competition contest :)

As a Newbie participant, I hope not to be Newbie again after this contest

As a tester, I would say this is a great Div. 4 Round.

As a tester, there will be a lot of wisdom bestowed upon you.

As a Newbie participant, I hope to be Pupil after this contest

My first unrated round! :)

As a gray participiant, I hope to be a LGM after this contest)

GL & HF

By the way, what is the difficulty of this game

Excited! I hope i will do well in this round.

As a tester, please stop posting cringe unfunny memes

Also the problems are pretty good

official participant with highest rating

Looking forward to my first out of competition round!

Dattebayo

First unrated contest

As a participant , I will test my speed through this contest

This is my first round as a TESTER. Wish you all the best & hope you will enjoy this round.

As a participant, I hope to be Specialist after this contest

Hoping to reach specialist after this contest!

After so many fuck ups DIV-4 is the only hope for me.

Thanks for creating these! Fridays are a bit complicated for me in schedule but it's still fun to participate and continue to learn. Look forward to this contest!

Excited to become Newbie for the first time !

Contests for all div 1,2,3,4 in the next 5 days...balanced, as all things should be

As a tester, it tasted like mother's cooking.

why only 120 minutes why note 135 minutes

Good luck to everyone

Hello everybody!

I wish you all good luck! I would like to become a student (green). I hope that the competition will be interesting.

Best, Jelal

Hoping to solve all problems!

hopefully i reach spec again after this

Hope it be my last rated div 4 contest

Alright, iron contest!!!

wait so Div. 4 is easier than Div. 3 (or Div. 2 (or Div. 1))? I thought the reverse, but seeing that this competition is rated for participants with rating $$$<1400$$$, and the previous one (with Vika) is for rating $$$<2000$$$ or something, I now think this round is gonna be easier..?

It's been 3 minutes without Div4, I can't stop shaking and I'm having serious mental breakdowns. I woke up today trying to log into Div4 but the site was down, I had a big panic attack but I managed to calm down after a few hours. I couldn't go to school today, I'm so worried that I even took my father's gun from the shed, thinking about killing myself. I am nothing without Div4, it's my life, it's my destiny, without Div4 I wouldn't be able to do anything. Div4 is the best thing ever made and I can't shake the addiction, it's the best oj out there. I can't stop shaking and crying, I'm so worried. I spent all my time on Div4, got rating and contribution.

I hope i become a specilast again

Bruh, my browser is always being checked. What's wrong?

div5

Problem set is good. The statements are short and easy to understand. A good div4 round...

My first *out of competition :)

My first rated competition.

i spent like 35 minutes on problem H, just to realize that i misread the question. literacy issue ngl. very good problemset btw :D

the first contest that I aked !!!

what was the upper bound for binary search of problem E?

Div 4.5

I really enjoyed this round. Hope not getting hacked :/

What's wrong here. I am pretty sure it's a graph problem(Last problem.)

ll n, m;
    cin >> n >> m;
    vector<array<ll, 3>> v;
    for(ll i = 0; i < m; i++){
        ll a, b, d;
        cin >> a >> b >> d;
        v.push_back({a, b, d});
    }
    vector<vector<vector<ll>>> adj(n + 1);    
    for(auto i: v){
        ll a = i[0];
        ll b = i[1];
        ll dist = i[2];
        if(dist >= 0) adj[a].push_back({b, dist});
        else adj[b].push_back({a, -dist});
    }
    ll ok = 1;
    vector<ll> vis(n + 1), dist(n + 1, 0);
    auto dfs = [&](ll x, ll y, auto dfs) -> void {
        for(auto c: adj[x]){
            if(c[0] == y) continue;
            if(vis[c[0]] == 0) {
                vis[c[0]] = 1;
                dist[c[0]] = dist[x] + c[1];
                dfs(c[0], x, dfs);
            }
            else{
                if(dist[c[0]] - dist[x] != c[1]){
                    ok = 0;
                }
            }
        }
    };
    for(ll i = 1; i <= n; i++){
        if(vis[i] == 0){
            dfs(i, -1, dfs);
        }
    }
    for(ll i = 0; i < m; i++){
        ll A = v[i][0]; ll B = v[i][1]; ll D = v[i][2];
        if(dist[B] - dist[A] != D){
            ok = 0;
        }
    }
    cout << (ok ? "YES" : "NO") << '\n';

can anyone help me out in the "F" problem , i got stuck in the 6th testcase, like shouldn't the answer be 6 when the trap is placed at position "24" Help me out!

this is my approach

int32_t main() {
    int t;
    cin >> t;
    while (t--) {
       int n;
       cin>>n;
       vector<int>nums(n ,0);
       unordered_map<int , int>m;
       for(int i=0 ; i<n ; i++) 
       {
           cin>>nums[i];
       }
       int ans=INT_MIN;
       int pos=0;
       for(int i=0 ; i<n ; i++)
       {
            int temp=n;
            int x=0;
            while(temp--)
            {
                cout<<x<<"  ";
                m[x]++;
                if(x!=0) 
                {
                    if(m[x]>=ans)
                    {
                        ans=m[x];
                        pos=x;
                    }
                }
                x+=nums[i];
            }
            cout<<endl;
       }
       
       cout<<"answer :"<<ans<<endl;
       cout<<"pos :"<<pos<<endl;
    }

    return 0;
}

Yo can someone pls help me out I dont get whats wrong with this code on problem 5. https://mirror.codeforces.com/contest/1850/submission/214926782

I tried to find the multiple that appeared the most, since that would catch the most frogs.

Hey, I am new to Code forces, can you explain these 2 points in little bit more detail please?

• 12-hour phase of open hacks after the end of the round (hacks do not give additional points)

• after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated

Is it so dumb to take too much time for the E (divide first would be the more suitable name for the problem)?

I couldn't solve E what's wrong here?

void solve(){ ll n; long long c; cin >> n >> c; vector arr(n, 0); ff(i, 0, n) cin >> arr[i];

ll sum = 0;
ll ss = 0;
ff(i, 0, n) ss += (arr[i] * arr[i]), sum += arr[i];

ll sq = sqrtl((sum * sum) - n * (ss - c));
cout << (sq - sum) / (2 * n) << nl;
return;

}

We want div-4 contest more often as beginer

best div 4 contest ever

Wow. That was nice contest. Overall, good problemset.

Good Problem Set. It seems that the difficulty difference between Div3 and Div4 is much higher than Div3 and Div2.

Thanx Man i Really enjoy this Round

good round, was too scared to implement dfs for H and ended up staring at it for 1 hour :(

What was the solution for G? My solution was to project all the points onto {1,0}{1,1}... all the directions. Group them into bins based on if they landed at the same point (after correcting for length of points), and then adding n choose 2 from each of those bins to ans. However, I got some error that I couldn't figure out if was due floating point inaccuracies or because my solution was wrong / nonsense.

Hi Coders, I have done the problem E, with a linear approach, which was very slow and then i thought about binary search but some test cases passed and some not. Please can someone advice on what is wrong with this code below ?

#include <bits/stdc++.h>
#include <iostream>
#include <vector>

using namespace std;

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

	int l = 0;
	int r = 1e9;
	int w = 0;
	while (l <= r) {
		w = l + (r - l) / 2;
		long long sum = 0;
		for (int i = 0; i < n; i++) {
			sum += ((2*w + a[i])*(2*w + a[i]));
		}
		if (sum == c) {
			break;
		} else if (sum < c) {
			l = w+1;
		} else {
			r = w-1;
		}
	}
	cout << w << "\n";
	return;
}

int main() {
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	int t;
	cin >> t;
	while (t--) {
		solve();
	}
}

Amazing contest!. Problems were clear and easy to understand. Difficulty was a bit easier than normal Div4, but great problems nonetheless. Thanks a lot SlavicG mesanu flamestorm and all testers.

Worst experience , either you make your platform better or just don't rate the contest, total time waste

Is Carrot working for anyone?

can someone explain the problem E like how the answer of 1st test case is 1

thanks....

editorial?

why this is an invalid input for F?: https://mirror.codeforces.com/contest/1850/hacks/931609/test I think because the output is bigger than 256 kb, but what to do if I want to test the limits?

My G got hacked (TL). Is it because of Python defaultdict? https://mirror.codeforces.com/contest/1850/submission/214881069

def solve():

ways = 0
n = int(input())

# read n points

xm = defaultdict(int)
ym = defaultdict(int)
sm = defaultdict(int)
dm = defaultdict(int)
points = []
for i in range(n):
    x, y = map(int, input().split())
    points.append((x, y))
    xm[x]+=1
    ym[y]+=1
    sm[x+y]+=1
    dm[x-y]+=1

for x,y in points:
    ways += xm[x] - 1
    ways += ym[y] - 1
    ways += sm[x+y] - 1
    ways += dm[x-y] - 1



return ways

https://mirror.codeforces.com/contest/1850/submission/214941507 Can anybody explain why am I getting TLE for problem F, isn't harmonic series nlogn?

Seems the only codeforces contest with highest participation and with highest problem a solver

Can someone hack my G or H?

My first AK contest on Codeforces!

I used binary search for problem-E but it has some error which I am unable to figure out. Can anyone please help me find error in my binary search logic for my submission 214950555. ? edit : when i set r = 1e10 the sample test-cases passed but on submission it fails again on some test case.

Me trying to solve problem E be like:
gimme smileys

Can anyone tell me where did i wrong in this code

t = int(input())

for _ in range(t):
    n, m = map(int, input().split())
    d = [[] for i in range(2 * n)];
    check = [False for i in range(2 * n)];
    checkpos = [-1e18] * (2 * n);
    def dfs(val, u):
        check[u] = True;
        checkpos[u] = val;
        res = True;
        #print(u, val)
        #print(u);
        for v in d[u]:
            #print(v[0], v[1]);
            if(checkpos[v[0]] != -1e18 and checkpos[v[0]] != val + v[1]):
                return False;
            if(check[v[0]] == False):
                #print(u, v);    
                res = res and dfs(val + v[1], v[0]);
        return res;
    def dfscheck(val, u):
        check[u] = True;
        res = True;
        for v in d[u]:
            if(not checkpos[v[0]] - checkpos[u] == v[1]):
                return False;
            if(check[v[0]] == False):
                res = res and dfscheck(val + v[1], v[0]); 
        return res;
    def dfsclear(u):
        check[u] = False;
        for v in d[u]:
            if(check[v[0]] == True):
                dfsclear(v[0]);
    ans = True;
    for i in range(m):
        a, b, dis = list(map(int, input().split()));
        d[a].append((b, dis));
        d[b].append((a, -dis));
    for i in range(1, n + 1):
        if(check[i] == False):
            ans = ans and dfs(0, i);
            dfsclear(i);
            ans = ans and dfscheck(0, i);
    print("YES" if ans else "NO");

if I haven't solved 5 problems in 5 contests am I unrated for this contest ?

Can someone please tell me why am I getting wrong answers for large test-cases Solution

Can someone explain how this $$$\mathcal{O}(n)$$$ solution gets TL? I mean, the constant must be big because of using unordered_maps but still... Is it the case?

https://mirror.codeforces.com/contest/1850/submission/214910960

Why my rating didn't change after this contest?

mesanu flamestorm