AtCoder Beginner Contest 358 Announcement

My post contest discussion stream for all problems

6 месяцев назад, # ^ |

that's not even the main thing , thing is output format could have been better , they just could have asked to output pair of cells which have wall between them

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nichke

6 месяцев назад, # ^ |

Yeah that's why I said implementing seemed messy. Format is weird. I didn't want to generate sequences of characters.

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GDCm1ro

6 месяцев назад, # |

← Rev. 10 →

What the fuck is the output format of problem F ???

What's the meaning of and the connected component containing the vertices (1,M) and (N,M) consists only of this path. ???

just for harder implementation ???

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harvey_wzy

6 месяцев назад, # ^ |

For human-readable

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aryanc403

6 месяцев назад, # |

← Rev. 2 →

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not_insync

6 месяцев назад, # |

26 correct 2 WA on C any idea submission

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SNX03

6 месяцев назад, # ^ |

Just go through every possibility $$$O(2^N)$$$

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MonoLith

6 месяцев назад, # ^ |

← Rev. 2 →

your way of computing minima is not correct

ex- 001 ,010,110

you only need shop 1 and 3 to fill the mask but your approach is greedy picking which is wrong and you will end up taking 1,2,3

hint-use bitmask

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_trie_again

6 месяцев назад, # |

any idea for g?

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ibrm

6 месяцев назад, # ^ |

you only stay in only one cell

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TrendBattles

6 месяцев назад, # ^ |

You try to go to a certain point on a board then just spam staying in that point.

Because of that, you can try to dp here, like dp[u][T] is the maximum value you will receive when you use T turns to go from start to u (all points here are converted into 1-D coordination).

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6 месяцев назад, # ^ |

is $$$T$$$ fixed for certain $$$U$$$?

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_trie_again

6 месяцев назад, # ^ |

I considered for max value cell only, will fix it

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Astaaaaaa

6 месяцев назад, # ^ |

← Rev. 2 →

But how do you calculate T ? I was lucky to get AC doing similar thing using BFS but just kept increasing turns till I got AC.

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TrendBattles

6 месяцев назад, # ^ |

T <= H * W I suppose so

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Astaaaaaa

6 месяцев назад, # ^ |

Yep but is there any proof on why T <= H * W. Is it because the number of unique paths from a cell to any other cell bounded by H * W ?

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aryanc403

6 месяцев назад, # ^ |

Try 1968D - Permutation Game first. You can use almost same arguments for this problem.

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Astaaaaaa

6 месяцев назад, # ^ |

Alright , Thank you !

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lvisbl_

6 месяцев назад, # ^ |

Same argument.. what do you mean, I still can not understand why the maximum number of steps to check is H*W and I can not find any formal proof, this drive me crazy.

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6 месяцев назад, # ^ |

f i x,y means when Takahashi goes i steps and stops at (x,y), how many fun value can he get.

Takahashi may walk for some steps and stopped at a position forever.

It's easy to solve f i x,y when i<=n*m. And it's can be proved that Takahashi may walk at most n*m times, so the answer is MAX (f i x,y + a x,y * (K-i))

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what's wrong in my solution of G?

6 месяцев назад, # |

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jeal0uspengu1n

6 месяцев назад, # ^ |

It's the same mistake that I did, and wasn't patient enough to even debug it after the contest so went through the editorial and just noticed that the dp table is going to have 3 states and I got what I was doing wrong, hope it provides you a hint :9

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6 месяцев назад, # ^ |

yo same case , I also wasn't patient enough to debug and watched the editorial and yeah missed the crucial no of turns state

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aryanc403

6 месяцев назад, # ^ |

← Rev. 2 →

Shortest path to reach final cell is not enough.
Consider this testcase -

Spoiler

5 5 1000
5 1
100 99 99 99 99
0 0 0 0 99
0 0 0 0 99
0 0 0 0 99
99 99 99 99 99

Answer is — 99989

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AnishchukT

6 месяцев назад, # ^ |

← Rev. 3 →

but A[i][j] > 0 (never mind)

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AnishchukT

6 месяцев назад, # ^ |

Thanks a lot!

This is somewhat that is in testcase9

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RE_Prince

6 месяцев назад, # |

how E?

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6 месяцев назад, # |

+23

Problem F is frustrating. I accept the other six problems quickly with no penalty, but I had wrong F for 5 times.

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zenoalt

6 месяцев назад, # |

← Rev. 2 →

[deleted]

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xiaofu15191

6 месяцев назад, # |

Why does the C++ solution in the problem E's editorial unavailable?

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xiaofu15191

6 месяцев назад, # ^ |

Oh,sorry,maybe my internet has some problems.It is now available.

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Igor_Parfenov

6 месяцев назад, # |

I think, I solved problem like today's F not long time ago, but don't remember, where. Anyone remember?

Also, what happened with problem G? I've never seen anything such simple on this position.

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nichke

6 месяцев назад, # ^ |

G could have easily been a D/E imo.

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BouncyHunter

6 месяцев назад, # |

Anyone could hack my F please? I have been testing on it for about 1 hour but I don't know why it gets WA*3.

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int maxn=100+10;
int n,m,k,a[maxn]; 
void solve(){
	cin>>n>>m>>k;
	if(k<n||(k&1)!=(n&1)) return cout<<"No"<<endl,void();
	int now=n;
	for(int i=1;i*2<=n;i++){
		if((k-now)/2<=m-1){
			a[i]=(k-now)/2;
			now=k;
			break;
		}
		a[i]=m-1,now+=m*2-2;
	}
//	for(int i=1;i*2<=n;i++) cout<<a[i]<<endl;
	if(now!=k) return cout<<"No"<<endl,void();
	int N=n*2+1,M=m*2+1;
	cout<<"Yes"<<endl;
	for(int i=1;i<=N;i++){
		if(i==1){
			for(int j=1;j<=M;j++) cout<<(j==M-1?'S':'+');
		}
		else if(i==N){
			for(int j=1;j<=M;j++) cout<<(j==M-1?'G':'+');
		}
		else if(i%2==0){
			for(int j=1;j<=M;j++){
				if(j==M||j==1) cout<<"+";
				else if(j%2==0) cout<<"o";
				else cout<<(m-j/2>a[(i-2)/4+1]?'|':'.');
			}
		}
		else{
			if((i/2)&1){
				for(int j=1;j<=M;j++){
					if(j&1) cout<<"+";
					else cout<<(m-j/2+1<=a[(i-2)/4+1]?'-':'.');
				}
			}
			else{
				for(int j=1;j<=M;j++){
					if(j&1) cout<<"+";
					else cout<<(j/2==m?'.':'-');
				}
			}
		}
		cout<<endl;
	}
}
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	int t=1;
//	cin>>t;
	while(t--) solve();
	return 0;
}

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wtc_fan

6 месяцев назад, # ^ |

+28

Your code fails when $$$n=3,m=5,k=13$$$. I am extremely sorry that you were disgusted by the authors!

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6 месяцев назад, # ^ |

← Rev. 3 →

+27

output:

Yes
+++++++++S+
+o.o.o.o.o+
+.+-+-+-+-+
+o|o.o|o|o+
+.+.+.+-+-+
+o.o|o.o.o+
+++++++++G+

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BouncyHunter

6 месяцев назад, # ^ |

+29

Thank you. I didn't notice that I can turn to the other side. And to be honest, I'm not disgusted XD anyway thanks a lot.

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https://atcoder.jp/contests/abc358/submissions/54597481

6 месяцев назад, # ^ |

+30

3 5 13 Yes +++++++++S+ +o.o.o.o.o+ +.+-+-+-+-+ +o|o.o.o.o+ +.+.+-+-+.+ +o.o|o|o|o+ +++++++++G+

It seems that you filled the path in maze one row by one row, however, when n is odd, you can also fill the last row but your code did not.

I also WA 3 for 5 times because of it, and it made me angry. However, after coming up with this situation, I accepted at once.

I have a friend who is rank 45, he didn't passed the following testcase but also accepted F in 67 minutes.

It is unfair, isn't it?

3 3 9 Yes +++++S+ +o.o.o+ +.+-+-+ +o|o.o+ +.+.+.+ +o.o|o+ +++++G+

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Jellyprx

6 месяцев назад, # ^ |

+23

You know that, I could pass the hack easily but I always got 1 RE.

Luck is always unpredictable

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crashsaladd

6 месяцев назад, # |

+11

Could someone please tell why my D fails ???

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MonoLith

6 месяцев назад, # ^ |

don't use it only stores unique element

let say a= 2,2,2,4,4,4

and b= 2,2

your approach will result in 2+4=6

but optimal one is 2+2=4

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MrCodder

6 месяцев назад, # ^ |

Use Multiset because element may repeat

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subhashgunda

6 месяцев назад, # |

+15

Can someone say why my Problem D is TLE Submission

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6 месяцев назад, # ^ |

+18

You should use ms.lower_bound(b[i])

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subhashgunda

6 месяцев назад, # ^ |

+10

can you please explain why does it make so much difference?

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6 месяцев назад, # ^ |

+10

set:: lowerbound is a binary search for red and black trees, with a complexity of O (log n).

std:: lower_bound for non randomly accessed containers, it is an iterator sequential search with a complexity of O (n).

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subhashgunda

6 месяцев назад, # |

Can someone please debug my Problem G(18xAC,18xRE)Submission

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6 месяцев назад, # ^ |

+10

1≤K≤10^9

You cannot open a vector whose size is related to K.

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tolbi

6 месяцев назад, # |

In problem F, O(n^2) is enough guys; all you have to do is do very little HOLY CASEWORK!!!

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cotx

6 месяцев назад, # ^ |

OTZ

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ZnPdCo

6 месяцев назад, # |

+15

Do they make AI more difficult to understand the statement by modifying important information in Problem F many times?

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6 месяцев назад, # ^ |

+10

That's right!

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6 месяцев назад, # ^ |

+14

I don't think so. I had never seen the input format or the output format when I was trying to solve Problem F because it's too long, but I still understand what the problem want me to do. I think AI is smart, and it may easily understand what did the problem mean. If AI can solve Problem F with correct information, it can also accept Problem F with wrong format.

ABC is for more than ten thousand people. If the question surface is wrong, it will make many people feel confusion. So I think it's no need to modifying importand information in order to make AI more difficult to understand Problem F.

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then00bprogrammer

6 месяцев назад, # |

E was such a good problem.

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skill_Issued

6 месяцев назад, # ^ |

How to do it ?

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then00bprogrammer

6 месяцев назад, # ^ |

← Rev. 3 →

It's DP+Combinatorics.

If you have n items, among which m are unique with quantities(q1, q2, q3... qm), the number of distinct ways to arrange these items is:

n!/(q1!*q2!...qm!) - (1)

Now for DP, there are two states [i,len] (i denotes the alphabet we're currently at and len denotes the length of our sequence so far).

Now, at each step, we attempt to take as many elements of that alphabet as possible. Therefore, the recurrence relation is:

dp[i][len]=sum(dp[i+1][len-j]*mod_inverse(j)) for j= 0 to min(c[i],len)

and base case is

dp[26][0]=1

For each state, by using mod_inverse at each step of calculation we've got denominator of eqn (1), to get the whole expression multiply it by len!.

Summation of dp[0][len] is your answer for len=1 to k.

Here's a link to my submission.

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skill_Issued

6 месяцев назад, # ^ |

← Rev. 2 →

Thanks mate.Amazing Solution.I appreciate your effort into writing this.

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XGptw

6 месяцев назад, # ^ |

yep it's good

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Pirate_King

6 месяцев назад, # |

Why does this TLE ??

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jose_5056

6 месяцев назад, # ^ |

Precompute the mod inverse for each $$${factorial_i}$$$.

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Pirate_King

6 месяцев назад, # ^ |

thx

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adaptatron

6 месяцев назад, # |

G is a nice follow up to the recent Atcoder problem : ABC344F : Earn to Advance. I also have a blog, hints and practice contest for the concepts used in the first problem.

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XGptw

6 месяцев назад, # ^ |

your articles are good.

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lvisbl_

6 месяцев назад, # ^ |

I dont see any relation between G and Time travel technique, can you help me to elaborate more?

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adaptatron

6 месяцев назад, # ^ |

It makes the observation trivial that there will only be one cell where you stay multiple cells. And this cell would be retrospectively fixed as the maximum valued cell that you encountered in your journey. Just like we did in ABC344F: Earn to Advance.

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_oO_Oo_

6 месяцев назад, # |

Can anyone tell me why am I having a TLE XD My code

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_oO_Oo_

6 месяцев назад, # ^ |

OK. I'm turning to C++.Same code in python and C++ led to 2209ms and 64ms.Almost got me crazy trying to optimize further in python :(

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Citypop

6 месяцев назад, # |

← Rev. 2 →

F is surprisingly neat if figure out the pattern, very fun to upsolve.

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cleanser

6 месяцев назад, # |

I don't like how I can go from TLE to a relatively fast AC in E simply by precomputing nck values.

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