Since the second round of this season of COCI (Croatian Open Competition in Informatics) was held [last saturday](https://mirror.codeforces.com/blog/entry/96881), here is the continuation in the series of COCI appreciation posts (I will post one after each COCI round, so six in total!). For my coaching, I went through all COCI contests since 2006 to gather tasks and selected some of my favorite ones. ↵
↵
### Notes↵
- Check out the [first post](https://mirror.codeforces.com/blog/entry/96205) for notes about the process and the problemset. ↵
- There are 9 tasks in this problemset since I accidentally forgot to put one task (Zoo) last time, so it's included now.↵
↵
### Tasks↵
↵
#### [A: 2016/2017, Contest 5: Ronald](https://evaluator.hsin.hr/tasks/HONI161756ronald/)↵
Author: Adrian Satja Kurdija ([user:satja,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
graph↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
graph task without any graph algorithms↵
</spoiler>↵
↵
Difficulty range: 1300-1500↵
↵
#### [B: 2011/2012, Contest 2: Kompići](https://evaluator.hsin.hr/tasks/HONI111226kompici/)↵
Author: Adrian Satja Kurdija ([user:satja,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
bitmask, combinatorics↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
creative use of bitmask to split numbers into buckets↵
</spoiler>↵
↵
Difficulty range: 1300-1500↵
↵
#### [C: 2013/2014, Contest 2: Putnik](https://evaluator.hsin.hr/tasks/HONI131426putnik/)↵
Author: Adrian Satja Kurdija ([user:satja,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
dp, nice state↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
a really nice state for a simpler dp task, it helped me solve [I from SEERC 2020](https://mirror.codeforces.com/gym/103102/problem/I)↵
</spoiler>↵
↵
Difficulty range: 1500-1700↵
↵
#### [D: 2020/2021, Contest 5: Planine](https://evaluator.hsin.hr/tasks/HONI202156planine/)↵
Author: Daniel Paleka and Paula Vidas ([user:valkyrie,2021-11-18],[user:paulica,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
convex hull, greedy↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
nice introduction to upper convex hull in a task where it’s easy to understand. finishes with least points to cover a set of intervals↵
</spoiler>↵
↵
Difficulty range: 1700-1900↵
↵
#### [E: 2013/2014, Contest 2: Linije](https://evaluator.hsin.hr/tasks/HONI131428linije/)↵
Author: Domagoj Ćevid↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
bipartite matching, game theory↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
simple task to practice bipartite matching, but showing a known game theory trick that connects matching with winning-losing positions. later used in [F from SEERC 2019](https://mirror.codeforces.com/group/77EwhNiBEM/contest/256946/problem/F)↵
</spoiler>↵
↵
Difficulty range: 1900-2100↵
↵
#### [F: 2019/2020, Contest 1: Trobojnica](https://evaluator.hsin.hr/tasks/HONI192016trobojnica/)↵
Author: Daniel Paleka ([user:valkyrie,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
constructive, triangulation↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
very mathsy task about triangulating a polygon. You are required to find a sufficient condition for the triangulation↵
</spoiler>↵
↵
Difficulty range: 2100-2300↵
↵
#### [G: 2014/2015, Contest 4: Stanovi](https://evaluator.hsin.hr/tasks/HONI141548stanovi/)↵
Author: Mislav Balunović ([user:mislav,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
adhoc dp↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
one trick dp where you are required to find the property of the given requirement. After that, a nice multidimensial dp problem↵
</spoiler>↵
↵
Difficulty range: 2100-2300↵
↵
#### [H: 2016/2017, Contest 6: Sirni](https://evaluator.hsin.hr/tasks/HONI161767sirni/)↵
Author: Domagoj Bradač ([user:DBradac,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
graph, mst, sieve of erathostenes, number theory↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
interesting trick using sieve of erathostenes and selecting fewer edges to run an algorithm on (similar to Svemir from last problemset)↵
</spoiler>↵
↵
Difficulty range: 2200-2400 (my guess :) ) ↵
↵
##Bonus task (since I forgot it last time):↵
↵
#### [2019/2020, Contest 1: Zoo](https://evaluator.hsin.hr/tasks/HONI192017zoo/)↵
Author: Ivan Paljak ([user:ipaljak,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
adhoc, graph, dfs↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
nice adhoc task that reduces to a graph. also appeared previously at [Baltic OI 2013](https://oj.uz/problem/view/BOI13_tracks)↵
</spoiler>↵
↵
Difficulty range: 2200-2400↵
↵
I hope you find these tasks useful!↵
↵
↵
↵
### Notes↵
- Check out the [first post](https://mirror.codeforces.com/blog/entry/96205) for notes about the process and the problemset. ↵
- There are 9 tasks in this problemset since I accidentally forgot to put one task (Zoo) last time, so it's included now.↵
↵
### Tasks↵
↵
#### [A: 2016/2017, Contest 5: Ronald](https://evaluator.hsin.hr/tasks/HONI161756ronald/)↵
Author: Adrian Satja Kurdija ([user:satja,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
graph↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
graph task without any graph algorithms↵
</spoiler>↵
↵
Difficulty range: 1300-1500↵
↵
#### [B: 2011/2012, Contest 2: Kompići](https://evaluator.hsin.hr/tasks/HONI111226kompici/)↵
Author: Adrian Satja Kurdija ([user:satja,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
bitmask, combinatorics↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
creative use of bitmask to split numbers into buckets↵
</spoiler>↵
↵
Difficulty range: 1300-1500↵
↵
#### [C: 2013/2014, Contest 2: Putnik](https://evaluator.hsin.hr/tasks/HONI131426putnik/)↵
Author: Adrian Satja Kurdija ([user:satja,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
dp, nice state↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
a really nice state for a simpler dp task, it helped me solve [I from SEERC 2020](https://mirror.codeforces.com/gym/103102/problem/I)↵
</spoiler>↵
↵
Difficulty range: 1500-1700↵
↵
#### [D: 2020/2021, Contest 5: Planine](https://evaluator.hsin.hr/tasks/HONI202156planine/)↵
Author: Daniel Paleka and Paula Vidas ([user:valkyrie,2021-11-18],[user:paulica,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
convex hull, greedy↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
nice introduction to upper convex hull in a task where it’s easy to understand. finishes with least points to cover a set of intervals↵
</spoiler>↵
↵
Difficulty range: 1700-1900↵
↵
#### [E: 2013/2014, Contest 2: Linije](https://evaluator.hsin.hr/tasks/HONI131428linije/)↵
Author: Domagoj Ćevid↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
bipartite matching, game theory↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
simple task to practice bipartite matching, but showing a known game theory trick that connects matching with winning-losing positions. later used in [F from SEERC 2019](https://mirror.codeforces.com/group/77EwhNiBEM/contest/256946/problem/F)↵
</spoiler>↵
↵
Difficulty range: 1900-2100↵
↵
#### [F: 2019/2020, Contest 1: Trobojnica](https://evaluator.hsin.hr/tasks/HONI192016trobojnica/)↵
Author: Daniel Paleka ([user:valkyrie,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
constructive, triangulation↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
very mathsy task about triangulating a polygon. You are required to find a sufficient condition for the triangulation↵
</spoiler>↵
↵
Difficulty range: 2100-2300↵
↵
#### [G: 2014/2015, Contest 4: Stanovi](https://evaluator.hsin.hr/tasks/HONI141548stanovi/)↵
Author: Mislav Balunović ([user:mislav,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
adhoc dp↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
one trick dp where you are required to find the property of the given requirement. After that, a nice multidimensial dp problem↵
</spoiler>↵
↵
Difficulty range: 2100-2300↵
↵
#### [H: 2016/2017, Contest 6: Sirni](https://evaluator.hsin.hr/tasks/HONI161767sirni/)↵
Author: Domagoj Bradač ([user:DBradac,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
graph, mst, sieve of erathostenes, number theory↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
interesting trick using sieve of erathostenes and selecting fewer edges to run an algorithm on (similar to Svemir from last problemset)↵
</spoiler>↵
↵
Difficulty range: 2200-2400 (my guess :) ) ↵
↵
##Bonus task (since I forgot it last time):↵
↵
#### [2019/2020, Contest 1: Zoo](https://evaluator.hsin.hr/tasks/HONI192017zoo/)↵
Author: Ivan Paljak ([user:ipaljak,2021-11-18])↵
↵
Tags: ↵
↵
<spoiler summary="Spoiler">↵
adhoc, graph, dfs↵
</spoiler>↵
↵
Note: ↵
↵
<spoiler summary="Spoiler">↵
nice adhoc task that reduces to a graph. also appeared previously at [Baltic OI 2013](https://oj.uz/problem/view/BOI13_tracks)↵
</spoiler>↵
↵
Difficulty range: 2200-2400↵
↵
I hope you find these tasks useful!↵
↵
↵
