2021 ICPC World Finals

12 problems from 2021 ICPC World Finals (contest 104288), difficulty -. 10/12 solutions verified against sample I/O.

12 items

2021 ICPC World Finals

ICPC/IOI | 12 problems | 10/12 verified | Difficulty - | 12m 55s

#	Problem	Time	✓
A	Crystal Crosswind	55s	✓
B	Dungeon Crawler	1m 6s	✓
C	Fair Division	1m 32s
D	Guardians of the Gallery	1m	✓
E	Hand of the Free Marked	1m 15s	✓
F	Islands from the Sky	50s	✓
G	Mosaic Browsing	1m 11s	✓
H	Prehistoric Programs	26s
I	Spider Walk	1m 17s	✓
J	Splitstream	51s	✓
K	Take On Meme	1m 8s	✓
L	Where Am I?	1m 24s	✓

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CF 104288L - Where Am I?

We are given a finite rectangular map of an otherwise infinite grid. Some cells contain markers and all other cells are empty. A person is placed at an unknown starting cell, but we only consider starting positions inside the given rectangle.

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CF 104288K - Take On Meme

The input describes a rooted tree where leaves are initial memes represented as 2D points. Every internal node represents a “vote” that merges its children into a new meme. At a leaf, the meme is fixed as a point $(x, y)$.

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CF 104288I - Spider Walk

We are given a circular spiderweb with n radial strands, numbered in order around the center. Between adjacent strands, there are m “bridges”, each placed at a unique distance from the center. A bridge connects two neighboring strands at that fixed radius.

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CF 104288J - Splitstream

We are given a directed acyclic network where every node either splits a single incoming sequence into two alternating streams or merges two incoming sequences into one alternating stream.

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CF 104288G - Mosaic Browsing

We are given a small pattern grid, called a motif, and a larger grid, called a mosaic. Each cell contains a color value, except that in the motif some cells are empty and behave like wildcards.

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CF 104288H - Prehistoric Programs

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CF 104288F - Islands from the Sky

Each island is a simple polygon lying on the ground plane, and each flight path is a 3D line segment with a positive altitude. A plane flies along that segment, and a downward-facing camera observes a strip of ground directly under the aircraft.

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CF 104288E - Hand of the Free Marked

We are given a deck split into several marking categories. Each category contains a known number of distinct cards, and the total deck size can be extremely large. A random group of $k$ cards is selected, and one of these $k$ cards is hidden face down.

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CF 104288D - Guardians of the Gallery

We are given a simple polygon representing the floor plan of a gallery. Inside this polygon there are two points: one is the guard’s starting position and the other is the center of a small circular sculpture.

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CF 104288C - Fair Division

Let $f^{D}(x1,dots,xn)=overline{f(overline{x1},dots,overline{xn})}$ and $f^{R}(x1,dots,xn)=f(xn,dots,x1)$. Composition yields $$f^{DR}(x)=overline{f(overline{xn},dots,overline{x1})},qquad f^{RD}(x)=overline{f(overline{xn},dots,overline{x1})},$$ so $f^{DR}=f^{RD}$ follows from…

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CF 104288B - Dungeon Crawler

We are given a weighted tree. Every query describes a scenario where a player starts at one room, must collect a special key located at another room, and must avoid permanently failing by entering a trap room before the key has been collected.

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CF 104288A - Crystal Crosswind

We are given a rectangular grid of size $dx times dy$. Each cell $(x, y)$ can either contain a molecule or be empty. The true arrangement is unknown, but we are given several “wind experiments” that partially reveal it.