SuntoryProgrammingContest2023（AtCoder Beginner Contest 321） Announcement

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SuntoryProgrammingContest2023（AtCoder Beginner Contest 321） Announcement

Автор atcoder_official, история, 15 месяцев назад, По-английски

We will hold SuntoryProgrammingContest2023 (AtCoder Beginner Contest 321).

Contest URL: https://atcoder.jp/contests/abc321
Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20230923T2100&p1=248
Duration: 100 minutes
Writer: physics0523, yuto1115, kyopro_friends, nok0, ynymxiaolongbao
Tester: nok0, MMNMM
Rated range: ~ 1999
The point values: 100-200-300-400-450-525-600

We are looking forward to your participation!

atcoder

atcoder_official
15 месяцев назад
53

Комментарии (44)

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FarDream

15 месяцев назад, # |

← Rev. 2 →

-21

I hope it can be simpler.

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VinCenzo___

15 месяцев назад, # |

How to do F?? giving tle at tc 66

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shadow9236

15 месяцев назад, # ^ |

← Rev. 2 →

Do knapsack in reverse for subtract operation

https://atcoder.jp/contests/abc321/submissions/45887808

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VinCenzo___

15 месяцев назад, # ^ |

Can you elaborate a little bit please.

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aryanc403

15 месяцев назад, # ^ |

+13

The main idea is -

Let's say the input is -

Let's say we have added nos in order [1,2,3,4,5], and now we want to delete 3 to have a knapsack dp count for [1,2,4,5].

Firstly, notice that the knapsack dp count for adding nos in order [1,2,3,4,5] and [1,2,4,5,3] will be the same.

So when we want to remove 3, we can assume that the insertion order was [1,2,4,5,3] instead of [1,2,3,4,5], because our dp values will be same for both order of insertions.
So for - 3, we should revert the operation required to do + 3, assuming + 3 was the last operation.

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Tyrant67

15 месяцев назад, # ^ |

I was not aware that this problem F will be so much easier. After seeing the problem now with you solution, now it seems that I could've solve this one during contest. But the mentality is, it always feels like the last problems probably the harder that's why don't open.

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shadow9236

15 месяцев назад, # ^ |

It is not necessary that a hard problem cannot have a simple solution

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aryanc403

15 месяцев назад, # ^ |

Good one. I assumed this would fail. I did Deleting from a data structure in $O(T(n)\log n)$
submission

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123asdf123

15 месяцев назад, # |

hard:(

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Tyrant67

15 месяцев назад, # |

Still struggling with C — 321-like Searcher At the end, I was able to figure out that the count will be 10, 45, 120, 210, 252, 210 etc. but can't able to code it. But overall the contest was good, the problems are quite fine.

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aryanc403

15 месяцев назад, # ^ |

← Rev. 2 →

Notice that in 321-like numbers, each digit can appear at max once.
Once we fix the possible digits, there will be a unique 321 no.

So the maximum possible no of 321-like numbers are $$$2^{10}$$$, generate all of them, sort them, and print kth value in the sorted array.

You can do it natively.

a={""}
Loop for 9
a={"",9}
Loop for 8
a={"",8,9,98}
Loop for 7
a={"",7,8,87,9,97,98,987}

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poplpr

15 месяцев назад, # ^ |

You can easily observe that in 321-number there are only one time appeared in any number of $$$9/8/7/6/5/4/3/2/1/0$$$. So if you want to enumerate all of $$$1024$$$ 321-number, you can enum $$$2^{10}$$$ states that each bit indicates this bit appears in the new number. And then just add them into one number.

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Sahil_32

15 месяцев назад, # ^ |

I feel ashamed :( https://atcoder.jp/contests/abc321/submissions/45864906

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tautology

15 месяцев назад, # ^ |

how did you hardcode? I mean obviously, you wouldn't have typed all the numbers manually.

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Sahil_32

15 месяцев назад, # ^ |

ran a program which iterates from 1 to 98766543210 and if it is a 321 number, output it to text file. Then copied all the numbers from the txt file

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tautology

15 месяцев назад, # ^ |

cool hack! how many minutes did you wait for the program to finish?

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Sahil_32

15 месяцев назад, # ^ |

~30-40s as far as i remember. depends on your pc ig

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anmolsainiii23

15 месяцев назад, # |

I found B Hard. For the very first time so much wrong submission on B

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chinesedfan

15 месяцев назад, # ^ |

Just brute force. Loop every possible value and check the sum. Or you can use binary search as stupid as me. https://atcoder.jp/contests/abc321/submissions/45828848

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poplpr

15 месяцев назад, # |

In problem F, why is the order of enumerating is $$$x, x + 1, \dots, K-1, K$$$ when the operation is -?

I can understand the traditional dp order of enumerating is $$$K, K-1, \dots, x + 1, x$$$ when the operation is +, but I can not understand the question above. T.T

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Misuki

15 месяцев назад, # ^ |

← Rev. 2 →

You can assume the last added element is x(since the order of adding element doesn't matters) and think of it as "undo" the last operation of adding element x, so you do everything reversely.

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poplpr

15 месяцев назад, # ^ |

Thanks, I got it!

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shadow9236

15 месяцев назад, # ^ |

← Rev. 2 →

dp[i] = number of ways of getting a subset sum of i. When removing x, you want to subtract the number of ways of obtaining i-x from dp[i] without using this x.

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Lovely_CatHxy

15 месяцев назад, # ^ |

Backward knapsack algorithm. Because $$$dp_i\to dp_{i+x}$$$ and continues, we need to first delete the contribution of smaller i to make sure that the we won't count extra contribution of x.

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moghit_ad

15 месяцев назад, # |

for D , can anyone tell why my code is failing

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llc5pg

15 месяцев назад, # ^ |

Did you consider a[i] > p ?

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no_oneplb

15 месяцев назад, # ^ |

← Rev. 3 →

In line 62, you need to check if (pos>0) ,then the code will get accepted.

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123asdf123

15 месяцев назад, # |

emm...My D solution is better than the editorial

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stefdasca

15 месяцев назад, # |

How to solve G?

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Misuki

15 месяцев назад, # ^ |

You may try (or just read the editorial) of this problem, since they are almost the same abc213-g

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stefdasca

15 месяцев назад, # ^ |

Oh wow thanks, didn't know about this problem before.

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SoyTony

15 месяцев назад, # ^ |

You can try LOCG which shows a classical way to do counting on connectivity.

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__HITman__

15 месяцев назад, # |

could any one tell me why my E get RE in two of the tests.my code

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__HITman__

15 месяцев назад, # ^ |

the question end, my poor minds.

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coderdhanraj

15 месяцев назад, # |

Thank you for the contest! finally became blue on Atcoder as well woo!
The problems were nice. (fun fact I solved C with digit dp and binary search)

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chromate00

15 месяцев назад, # |

← Rev. 2 →

-19

I would suggest that Ex-difficulty tasks should return to ABC. This being said, you may be wondering how it could be done in such a situation with a lack of hard tasks. Here is my idea. https://codeforces.net/blog/entry/120695

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