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Add BinarySearchUtils

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This commit is contained in:
OliBomby 2024-08-16 00:15:40 +02:00
parent 52c1858bbe
commit ac064e814f
2 changed files with 103 additions and 24 deletions
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28
osu.Game/Beatmaps/ControlPoints/ControlPointInfo.cs
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@ -230,32 +230,12 @@ namespace osu.Game.Beatmaps.ControlPoints
{
ArgumentNullException.ThrowIfNull(list);
if (list.Count == 0)
return null;
int index = BinarySearchUtils.BinarySearch(list, time, c => c.Time, EqualitySelection.Rightmost);
if (time < list[0].Time)
return null;
if (index < 0)
index = ~index - 1;
if (time >= list[^1].Time)
return list[^1];
int l = 0;
int r = list.Count - 2;
while (l <= r)
{
int pivot = l + ((r - l) >> 1);
if (list[pivot].Time < time)
l = pivot + 1;
else if (list[pivot].Time > time)
r = pivot - 1;
else
return list[pivot];
}
// l will be the first control point with Time > time, but we want the one before it
return list[l - 1];
return index >= 0 ? list[index] : null;
}
/// <summary>

99
osu.Game/Utils/BinarySearchUtils.cs Normal file
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@ -0,0 +1,99 @@
// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
using System;
using System.Collections.Generic;
namespace osu.Game.Utils
{
public class BinarySearchUtils
{
/// <summary>
/// Finds the index of the item in the sorted list which has its property equal to the search term.
/// If no exact match is found, the complement of the index of the first item greater than the search term will be returned.
/// </summary>
/// <typeparam name="T">The type of the items in the list to search.</typeparam>
/// <typeparam name="T2">The type of the property to perform the search on.</typeparam>
/// <param name="list">The list of items to search.</param>
/// <param name="searchTerm">The query to find.</param>
/// <param name="termFunc">Function that maps an item in the list to its index property.</param>
/// <param name="equalitySelection">Determines which index to return if there are multiple exact matches.</param>
/// <returns>The index of the found item. Will return the complement of the index of the first item greater than the search query if no exact match is found.</returns>
public static int BinarySearch<T, T2>(IReadOnlyList<T> list, T2 searchTerm, Func<T, T2> termFunc, EqualitySelection equalitySelection = EqualitySelection.FirstFound)
{
int n = list.Count;
if (n == 0)
return -1;
var comparer = Comparer<T2>.Default;
if (comparer.Compare(searchTerm, termFunc(list[0])) == -1)
return -1;
if (comparer.Compare(searchTerm, termFunc(list[^1])) == 1)
return ~n;
int min = 0;
int max = n - 1;
bool equalityFound = false;
while (min <= max)
{
int mid = min + (max - min) / 2;
T2 midTerm = termFunc(list[mid]);
switch (comparer.Compare(midTerm, searchTerm))
{
case 0:
equalityFound = true;
switch (equalitySelection)
{
case EqualitySelection.Leftmost:
max = mid - 1;
break;
case EqualitySelection.Rightmost:
min = mid + 1;
break;
default:
case EqualitySelection.FirstFound:
return mid;
}
break;
case 1:
max = mid - 1;
break;
case -1:
min = mid + 1;
break;
}
}
if (!equalityFound) return ~min;
switch (equalitySelection)
{
case EqualitySelection.Leftmost:
return min;
case EqualitySelection.Rightmost:
return min - 1;
}
return ~min;
}
}
public enum EqualitySelection
{
FirstFound,
Leftmost,
Rightmost
}
}