ICFPC 2016 Task Description
are artistic objects created by folding square papers into shapes,
without cutting or glueing. Origami also refers to the act of creating
Origami has been practiced for a long,
long time in Japan, and is now popular worldwide. But few are aware of
spiritual powers of origami. They offer protection from disasters such
as earthquakes, plagues and server failures.
Now, we want to enhance the Big Buddha Statue of Nara, by offering
enchanted origamis to the Buddha. Origami silhouettes of special
meanings are described in the Kojiki, an ancient scroll, but how to fold
them is lost knowledge.
As we are now in the 21st century of
industry 4.0, big data, and artificial intelligence, we employ drone
geishas to fold origamis. Your task is to recover the folds, each in
form of a mapping from a square of paper to a special silhouette, so
that the drone geishas can be programmed to fold the ancient origamis
described in the Kojiki.
To make matters worse, the very act of
folding origamis using drone geishas draws The Singularity near, that
clouds everything (also known as IoT) and makes it impossible to see the
future. In preparation for this, we need to find out more powerful
origami shapes that were not even predicted in the Kojiki. We need help
from all of you here; you are all hardworking programmers, so those
origami shapes that are insoluble by most of you must hold the strongest
We live in a two-dimensional world, so
only planar origamis are considered. As long as the origami is a valid
two-dimensional mapping, it is allowed to specify impossible folds, that require
papers to penetrate each other. Never mind, one of geisha's jobs is to
warp the reality into fourth dimension.
Sushi and sukiyaki will be rewarded. Wasshoi!
In our coordinate system, the x axis points to the right, y to the up. A two-dimensional point is specified
in the form a/b,c/d, where the numerators a, c are integers and
the denominators b, d are positive integers. The / and the denominator may be
abbreviated when the denominator is equal to 1. Fractions may be
Often we treat polygons and edges as sets
of points. In such cases the boundaries are inclusive. That is, a
polygon seen as a set of points includes its edges and vertices; an edge
as a set includes its two vertices.
The size of a problem file
or a solution file is defined by the number of non-whitespace ASCII
characters in it. This is to avoid the issue of newline-code differences
among operating systems, of newline characters at the end of file,
An interactive tool to
help you understand the idea of the task is provided at http://2016sv.icfpcontest.org/play
This tool is provided just for reference; it supports only simple valley
folds, so you may not be able to create some complex silhouettes with
this tool. The interactive tool is not part of the task description, and
the judges offer no guarantee of its consistency with the task
description. The judges will not use this tool to evaluate your
Figure 1. An origami silhouette with its
Each problem is specified
by a silhouette of the origami, which is a
two-dimensional figure, in ASCII text format. Additionally, a skeleton of the origami is given as a hint. For the exact definitions of silhouette and skeleton,
see the “Solution Evaluation” section.
A silhouette consists of one or more
polygons. In silhouette specifications, counterclockwise polygons refer
to polygons with positive area; clockwise polygons are treated as holes
in the silhouette.
A silhouette specification consists of the
following items, each in one line.
- for each polygon, the number
- for each vertex, its coordinates
A skeleton is a set of edges and folding line segments of the
origami. A skeleton is specified by the following items, each in one
- the number of line
- for each line segment, the coordinates of its
two vertices, separated by a space
specification must employ the least number of line segments; any two
line segments that lie on a same line must be disjoint.
Here is a sample problem specification which corresponds to
For a problem to be a
valid one, there must exist a valid and
normalized solution that produces the
silhouette and the skeleton exactly. The definitions for valid /
normalized solutions are given in the following sections.
(21:00 UTC, Aug 5)
Update: Problem submissions must be valid and normalized. On the other
hand, solution submissions must be valid but not necessarily
Figure 2. Visualization of facets of an
origami at their source (left) and destination (right) positions. The
alphabet labels represent the mapping of the vertices. This mapping
constitutes a solution to the origami problem in Figure
to a problem is a mapping that produces the
given silhouette. An origami consists of facet polygons created as results of folding the
square paper. All the components of origami such as the facet polygons,
their edges and vertices have two positions, one at source and the other at destination. The source position is where the paper is
a square located at (0,0), (1,0), (1,1), (0,1), and the destination position is where the paper is folded
to form the silhouette.
A solution specification consists of three
- the source positions part
- the facets part
- the destination positions
The source positions part
The vertices of an origami are indexed by integers starting
positions part consists of the following items, each in one
- for each vertex, its
The facets part
The facets part
consists of the list of facet polygons. Each polygon is specified by the
indices of the vertices.
For facet polygons, the vertices can either be listed in clockwise or
counterclockwise order. In both cases, facet polygons are treated as
polygons with positive areas.
The facets part
consists of the following items, each in one line:
each facet, the number of vertices, followed by the list of its vertex
indices, separated by single space characters.
In this part,
destination coordinates of the vertices are listed, in the ascending
order of the vertex index.
As an example, here is a solution that corresponds to the
above example problem.
4 0 1 5 4
4 1 2 6 5
3 4 5 3
3 5 6 3
and Normalized solution
solution is valid if and only if it satisfies all of the following
- All the source positions of the vertices
are within the initial square spanned by the four vertices (0,0), (1,0),
coordinate appears more than once in the source positions
- Any edge of any
facet has length greater than zero.
source positions, if two different edges share a
point, the point should always be one of the endpoints for both the
edges. That is, an edge touching another edge, or edges crossing each
other are prohibited.
facet polygons are simple; a facet polygon’s perimeter must not
- Every facet at
source position maps to its destination position,
by a congruent transformation that maps its source vertices to
corresponding destination vertices.
- At source position, the intersection set of any two different
facets has zero area.
- At source position,
the union set of all facets exactly matches the initial square.
- The size of the solution is no larger than Bs = 5000 Bytes.
Note that all facets are defined to have positive areas,
regardless of their perimeters being clockwise/counterclockwise, as
described in “The facets part” section.
A solution is normalized if and only if it
satisfies all of the following conditions:
- It is
- At source position, if two
different facets share an edge for a length greater than 0, then the
intersection set of those two facets at destination positions must have
an area greater than 0. In other words, if an edge separates two facets,
you should always fold the origami at that edge.
Conversely, the following properties of an origami are
irrelevant to its validity and normality:
- The skeleton
of the origami.
its destination silhouette fits within the source position (0,0), (1,0),
(1,1), (0,1) or not.
- Whether the destination position can be reached just by
folding the paper, or it requires parallel transformation and/or
rotation of the paper to be reached.
- Whether the paper is not folded at all.
Team Registration and
In this section
we explain the structure and schedule of the contest. We use the Contest
Clock to refer to the timings of various events in the contest. The
Contest Clock is set to 00:00 (CC) at the start of the contest, which is
00:00 (UTC) 5 August, 2016. The contest ends at 72:00
At 00:00 (CC) you can start team
registration on http://2016sv.icfpcontest.org/. You need to register your team to view problems and submit
The contest consists of two rounds. The
first 24 hours (00:00 (CC) - 24:00 (CC)) is the Lightning Round where
contestants can only submit solutions to those problems that are
described in the Kojiki. You don’t need to submit your source code at
the end of the Lightning Round.
The following 48 hours (24:00 (CC) - 72:00
(CC)) is the Full Round where contestants can also view and solve
problems created by other contestants. At the end of the Full Round, you
will be asked to submit your source code.
Every one hour, the
contest server reveals one problem per each team, starting at 24:00 (CC)
and till 69:00 (CC). Therefore, each team can publish a maximum of 46
problems. You can pre-register the problems you want to publish, and the
contest server automatically publishes them in the order you specified.
Pre-registration of the problems starts at 00:00 (CC). Remember, you
must submit a valid and normalized solution that produces the problem for your
problem submission to be accepted. The problem
specification will be automatically generated from the solution you have
A team cannot submit a solution to a
problem submitted by itself.
(21:00 UTC, Aug
5) Update: Solution submissions must be valid, but not necessarily be
normalized. Any invalid solution submissions are not
For an origami solution, its silhouette is the union set of all its facets at
the destination position. The skeleton of a solution is the union set of all the facet edges
at the destination positions.
Our goal is to approximate, and if
possible, reproduce the problem silhouette using your solutions. The
skeleton in the problem specification is just a hint, therefore the
skeleton of a solution is irrelevant for scoring.
Solutions submitted for a problem are
ranked by resemblance of
their silhouette to the problem silhouette. The resemblance of a valid
solution is calculated by the following formula:
resemblance = area_and /
- area_and is the area of
the intersection set of the solution silhouette and the problem
- area_or is the area of
the union set of the solution silhouette and the problem
Resemblance of each solution is
rounded down to six decimal places. Therefore, the highest resemblance attainable by an approximate solution is
Teams are ranked by team score. Teams can increase their scores both by
submitting problems and solutions. The team score is the sum of the
problem score and the solution score the team receives,
calculated as following.
perfect solution, that is, a solution with
resemblance = 1.0, is important in making high
scores. For a problem,
let s be the size of the problem(21:15 UTC, Aug 5) Update: let s
be the size of the solution that produced the problem and
n be the number of the
teams that submitted a perfect solution, plus 1. The problem-setting
team receives (5000 - s) /
n points, and each team that
submitted a perfect solution gets s / n points.
The scores for the teams with imperfect solutions are
calculated such that the total points earned by all the
imperfect solution teams is s / n, and each team's share is proportional to the resemblance of
its solution. Remember, you cannot submit a solution to your own
when 39 teams submitted a perfect solution to a 1000-bytes problem, the
problem-setting team will earn (5000 - 1000) / (39 + 1) =
100.0 points. Each team that submitted a
perfect solution will earn 1000 / (39 + 1) =
25.0 points, and each team that submitted an imperfect solution
will share the total of 1000 / (39 + 1) =
If you submit
multiple solutions to one problem, only the best one is used for
scoring. That is, the solution with the highest
resemblance, and in case of a tie, the solution with the smallest
The team with the highest team score is the
winner of the contest. In case of a tie, the sum of the sizes of the
scoring solutions is calculated for each team. The team with smaller
total size will win.
Rate Limits and Leaderboard Freeze
A team may not make more than 1000 submissions per hour (both
the problem and the solution submissions count.) That is, a team
can make up to 1000 submissions during 00:00 (CC) - 01:00 (CC),
1000 submissions during 01:00 (CC) - 02:00 (CC), and so on. Also,
the period between two consecutive submissions must be greater
than 1 second. The judges will update the problem list and the ranking
every hour, so kindly refrain from refreshing too frequently. The
leaderboard will be updated till 66:00 (CC); after that the leaderboard
will be frozen, and the final results will be published at ICFP
2016. The statistics for each problem will be updated till the end of
Please submit your
clarifications and questions as comments to this blog article. In order
to provide consistent answers to all contestants, and to make the
questions and answers easier to find, we kindly wish your cooperation in
using this method of asking questions.
By registration, ICFP
programming contest (ICFPC) participants understand and agree
to the following terms and
participants retain ownership of all intellectual property rights in and
to any submitted solutions, source codes, custom tools, and related
materials ("submissions") that participants had before submission. As a
condition of entry, participants grant ICFPC judges a non-exclusive,
perpetual, irrevocable, worldwide, royalty-free license to use,
reproduce, publish, distribute, publicly perform, and publicly
display the submissions for the purposes of allowing ICFPC judges to
test and evaluate the submissions for purposes of the
may only be member of a single team, and teams may not divide or
collaborate with each other once the contest has begun. As long as
contest participants follow these terms and conditions, and
applicable laws, there is no limitation to the
number of members in a single team, and contest participants may use
whatever programming languages and computer resources.
Although the judges take
the best effort to keep the contest server running, the server is not
guaranteed to be available all time throughout the contest. In
particular, the server may be temporarily unavailable, or available at
lowered submission rate limits, due to server maintenance, server
resource constraints or other reasons. Judges are not obliged to take
any compensation measures in such cases.
judges retain the right to monitor, record, and investigate the
submissions, other contest-related activities, or lack thereof, of
participants. The records are used for the sole purpose of judgement and
are discarded once the contest-related events are over. Violations of
these terms and conditions, any attempts to compromise the integrity of
the contest infrastructure, attempts to interfere with other
participants, attempts to spoil the joy and spirit of the contest will
lead to disqualification of the involved participants and revocation of
the related scores and prizes. The decisions of the judges on these
matters are final. There is no right of appeal. In case of dispute, the
judges retain the right to send ninjas to you to “resolve” the issue.