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Merge pull request #18067 from smoogipoo/reduce-diffcalc-sort-complexity

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Reduce sorting worst-case time complexity in difficulty calculation
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Dean Herbert 2022-05-03 21:49:44 +09:00 committed by GitHub
commit 054a82d152
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3 changed files with 17 additions and 3 deletions
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6
osu.Game.Rulesets.Osu/Difficulty/Skills/OsuStrainSkill.cs
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@ -38,7 +38,11 @@ namespace osu.Game.Rulesets.Osu.Difficulty.Skills
double difficulty = 0;
double weight = 1;
List<double> strains = GetCurrentStrainPeaks().OrderByDescending(d => d).ToList();
// Sections with 0 strain are excluded to avoid worst-case time complexity of the following sort (e.g. /b/2351871).
// These sections will not contribute to the difficulty.
var peaks = GetCurrentStrainPeaks().Where(p => p > 0);
List<double> strains = peaks.OrderByDescending(d => d).ToList();
// We are reducing the highest strains first to account for extreme difficulty spikes
for (int i = 0; i < Math.Min(strains.Count, ReducedSectionCount); i++)

8
osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyCalculator.cs
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@ -141,7 +141,13 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
double colourPeak = colourPeaks[i] * colour_skill_multiplier;
double rhythmPeak = rhythmPeaks[i] * rhythm_skill_multiplier;
double staminaPeak = (staminaRightPeaks[i] + staminaLeftPeaks[i]) * stamina_skill_multiplier * staminaPenalty;
peaks.Add(norm(2, colourPeak, rhythmPeak, staminaPeak));
double peak = norm(2, colourPeak, rhythmPeak, staminaPeak);
// Sections with 0 strain are excluded to avoid worst-case time complexity of the following sort (e.g. /b/2351871).
// These sections will not contribute to the difficulty.
if (peak > 0)
peaks.Add(peak);
}
double difficulty = 0;

6
osu.Game/Rulesets/Difficulty/Skills/StrainSkill.cs
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@ -100,9 +100,13 @@ namespace osu.Game.Rulesets.Difficulty.Skills
double difficulty = 0;
double weight = 1;
// Sections with 0 strain are excluded to avoid worst-case time complexity of the following sort (e.g. /b/2351871).
// These sections will not contribute to the difficulty.
var peaks = GetCurrentStrainPeaks().Where(p => p > 0);
// Difficulty is the weighted sum of the highest strains from every section.
// We're sorting from highest to lowest strain.
foreach (double strain in GetCurrentStrainPeaks().OrderByDescending(d => d))
foreach (double strain in peaks.OrderByDescending(d => d))
{
difficulty += strain * weight;
weight *= DecayWeight;