Hello Everyone!

The 18th Japanese Olympiad in Informatics Final Round Online Contest will be held on February 10. (01:00 — 05:00 GMT).

The contest duration is 4 hours. There are five problems, which are the same as the 18th JOI Final Round. Problem statements will be provided both in Japanese and English.

The registration page will be announced 30 minutes before the contest start.

You can see details in the contest information page.

Hello everyone!

JOI Open Contest 2018 will be held on July 8. (04:00-09:00 GMT) and July 8. (10:00-15:00 GMT) .The tasks for Round 1 and Round 2 are the same. So you can choose the round you will participate in.

The main purpose of this contest is to give an opportunity to Japanese delegations and candidates of delegations for training and practice for IOI. But the contest itself is open to everybody. Everybody is welcome to attend JOI Open Contest 2018!

The contest duration is 5 hours and there will be 4 problems. Each submitted source program must be written in either C++, Pascal, or Java. Problem statements will be provided both in Japanese and English.

Details are available in contest information.

The past contest information is available in JOI Website.

Good luck and have fun!

UPD1 I uploaded the editorials, sample source codes, and input/output data in the contest information page.

Hello Everyone!

Japanese Olympiad in Informatics Spring Camp 2018 will be held from Mar. 19 to Mar. 25.

There will be four online mirror contests during the camp.

• day1 : Mar. 20 (00:30 — 05:30 GMT)
• day2 : Mar. 21 (00:30 — 05:30 GMT)
• day3 : Mar. 22 (00:30 — 05:30 GMT)
• day4 : Mar. 23 (00:30 — 05:30 GMT)

The contest duration is 5 hours and there are 3 to 4 problems in each day. Problem statements will be provided both in Japanese and English.

There might be unusual tasks such as output-only tasks, optimization tasks, reactive tasks and communication tasks, just like International Olympiad in Informatics (IOI).

The contest site and registration form will be announced about 30 minutes before the contest.

Details are available in the contest information page.

We welcome all participants. Good luck and have fun!

Hello Everyone!

The 17th Japanese Olympiad in Informatics Final Round Online Contest will be held on 11 Feb. (00:30 — 04:30 GMT).

The contest duration is 4 hours and there will be 5 problems, which is the same as the 17th JOI Final Round. Problem statements will be provided both in Japanese and English.

The registration page will be announced 30 minutes before the contest. I will update this blog post then.

You can see details in the contest information page.

UPD: The contest has postponed 30 minutes due to a technical issue. Sorry for inconvenience.

UPD2: The contest site is open. You can register now.

UPD3: The contest is over. Currently, the contest is in analysis mode. You can submit your codes through the contest site unofficially. The official result and the contest materials (input/output, official editorial, official answer code) will be distributed later.

Hello everyone!

JOI Open Contest 2017 will be held on July 2. (04:00-09:00 GMT) and July 2. (10:00-15:00 GMT) .The tasks for Round 1 and Round 2 are the same. So you can choose the round you will participate in.

The main purpose of this contest is to give an opportunity to Japanese delegations and candidates of delegations for training and practice for IOI. But the contest itself is open to everybody. Everybody is welcome to attend JOI Open Contest 2017!

The contest duration is 5 hours and there will be 3 problems. Problem statements will be provided both in Japanese and English.

Details are available in contest information .

The past contest information is available in JOI Website .

Good luck and have fun!

UPD: The round1 will start in 90 minutes. The contest site and registration form will be announced 30 minutes before the contest.

UPD2: The contest is over. Thank you for your participation! Now, you can get problem statements, editorials and test data from contest information . Also, we open judge for analysis for about 24 hours from now. contest page is here .

We are carrying out the questionnaire to improve our contests. Please tell me your impressions about the contest. You can access the questionnaire sheet here . Thank you for your cooperation.

UPD3: The judge program for amusement_park was wrong in the contest as mentioned in this blog comment. Now, you can use the correct judge in the analysis round. We extend the analysis round 24 hours (The end of the round is 7/5 01:00 GMT) . You can also get the correct judge program from the test data section. We are very sorry for this issue.

Hello Codeforces!

Japanese Olympiad in Informatics Spring Camp 2017 will be held from Mar. 19 to Mar. 25.

There will be four online mirror contests during the camp.

• day1 : Mar. 20 (00:30 — 05:30 GMT)
• day2 : Mar. 21 (00:30 — 05:30 GMT)
• day3 : Mar. 22 (00:30 — 05:30 GMT)
• day4 : Mar. 23 (00:30 — 05:30 GMT)

The contest duration is 5 hours and there are 3 to 4 problems in each day. Problem statements will be provided both in Japanese and English this year.

There might be unusual tasks such as output-only tasks, optimization tasks, reactive tasks and communication tasks, just like International Olympiad in Informatics (IOI).

Details are available in contest information.

Good luck and have fun!

UPD1:

We will use CMS (customized version) on our server to hold the contests. The registration URL will be announced just before the first contest.

Providing English statements is our first trial for this year, so there aren't past English problems. If you try past problems with Google Translate, you can get them from here.

UPD2:

Registration is available now.

• Contest page : http://cms.ioi-jp.org/contest/
• Ranging : http://cms.ioi-jp.org/ranking/

UPD3:

The contests are over. The judge is open now. You can submit your codes in the contest page.

Unofficial Simple Editorial:

• cultivation: East and West wind have almost the same effect. You don't have to consider the order. The essential value is the sum of the number of east and west wind. The candidates of this value are O(N²). You can easily calculate how many north wind and south wind needed to fill each column. The number of the essential columns are O(N). So you can solve this by O(N³logN) or O(N³) with precalculate.
• port facility: Let's assume the containers nodes and make edges between the nodes which can't put on the same area. If this graph is bipartite, The answer is 2^(#connected compornent). Otherwise, the answer is 0. First, count the connected component. Sort containers and use Segmenttree, then you can BFS with O(NlogN). You can check wheather the graph is bipartite by just simulating the transportation.
• sparklers: The first insights are you can do binary search the answer v, no two persons don't have to burn sparklers simultaneously and burning sparklers looks like an interval. If you can merge [l, r - 1] or [l + 1, r] and (X_r - X_l) / v ≤ (r - l)T, then you can merge [l, r). You can do some greedy algorithm to check you can merge [0, n)
• arranging tickets: Open the circle at point 0. You can use binary search by determining the answer m. You don't have to flip the interval [a, b], [c, d] such that a < b < c < d. So Filipped interval share some point t. Let's determin t and the number of flipped interval n. Actually, the candidate of n is a_t - m and a_t - m + 1. ( a_i is the sum of initial passengers through point i), the candidate of t is leftmost and rightmost argmax a_i. You can greedily determin flipped intervals.
• broken device: Divide bits into groups of size 3. There is a code of 3bits that translate 2 bit if intact, 1bit if 1 bit lost, 0 bit if more bits lost.
• railway trip: If you make edges to adjacent greater stations, It looks like a tree. You can use doubling to answer queries quickly.
• coach: Sort refilling points by S_imodT and passengers by by D_i together. Each adjacent refilling points can purge passengers between them from the back. You can do DP and you can fasten DP by convex hull trick.
• long mansion: Let Llink_i be the rightmost j s.t. j ≤ i and c_i is in A_j. Rlink_i is alike. Then JOI-kun can't go out from [l, r] iff Llink_r < l and r < Rlink_l. Let Lret_r be min{ l | Llink_r < l and r < Rlink_r }. Then JOI-kun can't go from L to R iff there exists r s.t. L ≤ r < R and Lret[r] ≤ L. You can use segtree to speed it up.
• natural park: Let's consider the case of tree. You can add node one by one. First, you can determin wheter the node connects currect tree directly. If Yes, Number the tree nodes BFS order, then you can binary search which node connects the node directly. If No, binary serch a node between this node and the current tree, and solve recursively. In the case of general graph, you can solve with almost the same solution.
• abduction 2: Memoize. If you speed up finding the street with sparse table, you can get AC. Time complexity analysis is a little complicated. This margin is too narrow to contain. If you want to know, you shold read the Japanese editorial slide.
• city: Index the nodes by euler-tour order. Encode nodes by pair of the id and interval length. Sum of the number of the descendants of each nodes are at most 18 N. So most of the lengths are very small. Representing length like 1.05ⁿ ( if you can't, add dummy nodes ) is very efficient in this case.
• dragon 2: Sort points by the angles from X. sweep them by the angle. Use segtrees or BITs to manage current points by the order of the angle from Y. You can now answer queries efficiently. Sqrt decompose queries by the size, you can solve with O(NsqrtQlogN)

UPD4:

The score distribution and official editorial slides (Japanese) are distributed.

https://www.ioi-jp.org/camp/2017/2017-sp-tasks/index.html

Hello Codeforces!

The 16th Japanese Olympiad in Informatics Final Round Online Contest will be held on 12 Feb. (00:30 — 04:30 GMT).

The contest duration is 4 hours and there will be 5 problems, which is the same as the 16th JOI Final Round. Problem statements will be provided both in Japanese and English this year.

Details are available in contest information .

Good luck and have fun!

UPD: Registration is available now.

UPD2: Judge server is open now. You can submit your solutions. You need remake your account to use judge.

UPD3: Editorial will be provided only in Japanese. Judge data and sample source codes will also be provided.