Contest Formats

A comparison of LCOJ's 7 contest formats (scoring, tie-breaking, penalties, scoreboard freeze) and how to configure each one.

⏱ ~15 min read · 👤 Contest organisers · 🔑 Permission to edit the contest in the admin

When you need this page

Use this page when you create a contest and have to pick its scoring rules, or when contestants ask why the scoreboard is ordered the way it is. If you have never created a contest, start with Contest setup.

A contest format decides how points are calculated and how ties are broken on the scoreboard. LCOJ ships 7 formats, inherited from DMOJ and VNOJ.

Which format should I pick?

Key (format_name)	Display name	Score per problem	Tie-break	Default penalty	Scoreboard freeze	Problem labels	Good for
default	Default	Best score	Sum of last submission times on scored problems	None	No	1, 2, 3…	Practice rounds, simple contests
ioi	IOI (pre-2016)	Best score of a single submission	Optional (default: no tie-break)	None	No	1, 2, 3…	Old-style IOI, problems without subtasks
ioi16	IOI	Sum of the best score of each subtask across all submissions	Optional (default: no tie-break)	None	No	1, 2, 3…	Olympiad-style contests with subtasks
ecoo	ECOO	Last submission's score + bonuses	Optional (default: no tie-break)	None (bonuses instead)	No	1, 2, 3…	Contests that reward early solves
atcoder	AtCoder	Best score	Time of last score change + penalty	5 min per wrong try	No	1, 2, 3…	AtCoder-style contests
icpc	ICPC	Best score	Total time + penalty, then time of last solve	20 min per wrong try	Yes	A, B, C…	ICPC-style team contests
vnoj	VNOJ	Best score	Total time + penalty (or last solve only with LSO), then time of last solve	5 min per wrong try	Yes	1, 2, 3…	VNOJ/Codeforces-style contests that need a frozen scoreboard

Quick picks

• A regular contest with no penalties: default.
• Problems with subtasks and partial scoring: ioi16.
• Penalize wrong submissions and freeze the scoreboard near the end: vnoj (time in seconds, numeric labels) or icpc (time in minutes, letter labels).

Setting the format

The format is configured in the Django admin (Admin → Contests → pick a contest), in the Format section:

Field	Admin label	Meaning
format_name	contest format	One of the keys in the table above. Defaults to default.
format_config	contest format configuration	A JSON object with the format's options. Leave empty to use the defaults.
frozen_last_minutes	frozen last minutes	Number of minutes before the end during which the scoreboard is frozen. Only works for icpc and vnoj. 0 = no freeze.
problem_label_script	contest problem label script	(Optional) A Lua function that generates problem labels, overriding the format's default labels.

A few related fields:

• points_precision (default 3): number of decimal digits scores are rounded to.
• show_short_display (show short form settings display): shows a summary of the format's scoring rules on the contest page.

format_config validation rules (for every format that takes options):

• It must be a JSON object (or empty).
• Keys that the format does not know are rejected (unknown config key). You cannot mix options from several formats into one config.
• Value types must match the default: an integer (5, not 5.0) or a boolean (true/false).
• default only accepts an empty config (null or {}).

Full rescore

When you save a contest and format_name, format_config or frozen_last_minutes changed, LCOJ recalculates every participation. On a large contest this can take a while.

How ranking works

Every format stores three values per participant: score (score), cumulative time (cumtime) and a tie-breaker (tiebreaker). The scoreboard is sorted by:

1. Disqualified participants always go last.
2. score, descending.
3. cumtime, ascending.
4. tiebreaker, ascending.

Participants equal on all three values share a rank. Formats differ only in how they compute these values.

In the sections below, a submission's "time" is the number of seconds (minutes for icpc) since the participant started. "Wrong tries" only count judged submissions: compile errors (CE) and internal errors (IE) are not counted.

Default (default)

Scoring: each problem's score is the best score among your submissions; your total is the sum over problems.

Tie-break: cumtime = sum of the time of your last submission on each problem with a non-zero score. Submitting again to a problem you already scored on (even without improving) increases your time.

Configuration: none. format_config must be empty.

Example:

Participant	Problem 1	Problem 2	Problem 3	Total	cumtime
Alice	100 (last submit at 10 min)	80 (25 min)	60 (40 min)	240	75 min
Bob	100 (15 min)	80 (20 min)	60 (35 min)	240	70 min

Bob ranks higher because his total time is lower.

IOI (pre-2016) (ioi)

The legacy IOI format: each problem takes the score of your single best submission (subtask scores are not combined across submissions).

Configuration:

Option	Type	Default	Meaning
cumtime	boolean	false	Break ties by the sum of the times you first reached your best score on each scored problem.
last_score_altering	boolean	false	Break ties by the time of your latest score-changing submission.

cumtime	last_score_altering	Tie-break
false	false	None: equal scores share a rank.
true	false	Sum of the times you reached your best score on each problem.
false	true	Time of the last score-changing submission.
true	true	Sum of times, then time of the last score-changing submission.

{
  "cumtime": true,
  "last_score_altering": false
}

IOI (ioi16)

The IOI format used since 2016: for each subtask (test batch), LCOJ takes your best score on that subtask across all fully judged submissions, then adds them up to get the problem score.

Use it only for problems with subtasks

This format works per batch. Test cases outside any batch are lumped into a single group, which is usually not what you want. Group the tests of every problem in the contest into batches (see Problem Format).

Example: a problem with 2 subtasks (30 and 70 points):

Submission	Subtask 1	Subtask 2	Submission score
#1	30	0	30
#2	0	70	70
Problem score	30	70	100

Configuration:

Option	Type	Default	Meaning
cumtime	boolean	false	Break ties by total time. A problem's time is the latest of the times you first reached your best score on each of its subtasks.

With cumtime set to false, equal scores share a rank. ioi16 does not accept last_score_altering.

{
  "cumtime": true
}

INFO

Contests using ioi16 cannot be replayed (scoreboard replay).

ECOO (ecoo)

Scoring: each problem takes the score of your last submission (ignoring CE and IE), plus bonuses. Bonuses only apply when that last submission scored more than 0:

• First-try bonus: if you have exactly one submission on the problem (not counting CE/IE) and it got full points, you get first_ac_bonus extra points.
• Time bonus: you get ⌊minutes left in your contest window ÷ time_bonus⌋ extra points.

Configuration:

Option	Type	Default	Meaning
cumtime	boolean	false	Break ties by the sum of your last submission times on all problems (including 0-point ones).
first_ac_bonus	integer ≥ 0	10	Bonus for getting AC on the first try.
time_bonus	integer ≥ 0	5	+1 point for every time_bonus minutes before the end of your window. 0 disables it.

{
  "cumtime": false,
  "first_ac_bonus": 10,
  "time_bonus": 5
}

Example: your last submission scores 50/100 with 23 minutes left and time_bonus = 5: bonus ⌊23 ÷ 5⌋ = 4, problem score = 54. No first-try bonus because it wasn't full points.

AtCoder (atcoder)

Scoring: best score on each problem.

Penalty: on each problem with a non-zero score, every submission (excluding CE/IE) before the first one that reached the best score costs penalty minutes. Problems with 0 points are not penalized (the number of tries is still shown).

Tie-break: cumtime = the latest of the times you reached your best score (your last score change) + total penalty.

Configuration:

Option	Type	Default	Meaning
penalty	integer ≥ 0	5	Penalty minutes per wrong try. 0 disables penalties.

{
  "penalty": 5
}

Example: problem 1 reaches full score at 10 min (0 wrong tries), problem 2 at 25 min (2 wrong tries), problem 3 at 50 min (1 wrong try). cumtime = 50 + 3 × 5 = 65 min.

ICPC (icpc)

Scoring: best score on each problem. For classic ICPC rules (count solved problems), give every problem 1 point and disable partial scoring.

Penalty: same as AtCoder, 20 minutes by default for each wrong try before the first best-score submission.

Tie-break:

1. cumtime = sum of the times (in minutes, rounded down) you reached your best score on scored problems + total penalty.
2. tiebreaker = the latest of those times.

Problem labels: A, B, …, Z, AA, AB…

Scoreboard freeze: supported (see below).

Configuration:

Option	Type	Default	Meaning
penalty	integer ≥ 0	20	Penalty minutes per wrong try. 0 disables penalties.

{
  "penalty": 20
}

Example:

Problem	Solved at	Wrong tries	Penalty
A	10 min	0	0
B	25 min	2	40
C	50 min	1	20

cumtime = 10 + 25 + 50 + 60 = 145 min, tiebreaker = 50.

VNOJ (vnoj)

A format developed by VNOJ. It is close to ICPC but measures time in seconds, uses a lighter penalty and can count only the last solve.

Scoring: best score on each problem.

Penalty: on each scored problem, every submission (excluding CE/IE) before the first best-score submission costs penalty minutes.

Tie-break:

1. cumtime = sum of the times you reached your best score on scored problems + total penalty. With LSO on, only the latest of those times is used instead of the sum.
2. tiebreaker = the latest of those times.

Problem labels: 1, 2, 3…

Scoreboard freeze: supported. For problems with submissions after the freeze, the scoreboard shows the pre-freeze result plus the number of pending submissions. If the participant already had full points before the freeze, the real result is shown.

Configuration:

Option	Type	Default	Meaning
penalty	integer ≥ 0	5	Penalty minutes per wrong try. 0 disables penalties.
LSO	boolean	false	Last Submission Only: cumtime uses only the latest best-score time, not the sum.

{
  "penalty": 5,
  "LSO": false
}

Example: the ICPC example data with penalty = 5: total penalty = 3 × 5 = 15 min.

• LSO = false: cumtime = 10 + 25 + 50 + 15 = 100 min.
• LSO = true: cumtime = 50 + 15 = 65 min.

Scoreboard freeze

Only icpc and vnoj support freezing. Set frozen last minutes (frozen_last_minutes) to a value greater than 0 to turn it on. Example with frozen_last_minutes = 60:

• From end time − frozen_last_minutes on, participants and visitors only see results of submissions made before that moment.
• Users who can edit the contest (authors, curators) always see the real scoreboard.
• The scoreboard stays frozen after the contest ends. To reveal the results, set frozen_last_minutes back to 0 and save; LCOJ recalculates the scoreboard.
• While frozen, the contest's full submission list is hidden from users who cannot edit the contest.
• Only contests with frozen_last_minutes = 0 can be replayed.

Troubleshooting

Symptom	Fix
Saving the contest fails with unknown config key	format_config contains a key the selected format does not know. Use only that format's options.
format_config is rejected although the keys are right	Value types must match the defaults: integers as 5 (not 5.0), booleans as true/false.
The config cannot be saved with default	default only accepts an empty config (null or {}).
The contest has ended but the scoreboard is still frozen	Set frozen_last_minutes = 0 and save to reveal the real scoreboard.
There is no scoreboard replay	Replay is only available when frozen_last_minutes = 0 and the format is not ioi16.
The scoreboard does not change right after switching format	LCOJ is recalculating every participation; large contests can take a while.

Next steps

• Contest setup: create a contest, add problems, invite contestants.
• Your first contest: a step-by-step walkthrough from start to finish.
• Contest data download: export submissions after the contest.