110 lines
2.8 KiB
C#
110 lines
2.8 KiB
C#
using System;
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using System.Collections;
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using System.Collections.Concurrent;
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using System.Collections.Generic;
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using System.Linq;
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using System.Threading;
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using UnityEngine;
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namespace XericLibrary.Runtime.MacroLibrary
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{
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public static partial class MacroMath
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{
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#region 洗牌算法
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/// <summary>
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/// Fisher-Yates洗牌算法，时间复杂度为O(n*n),空间复杂度为O(n)
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/// </summary>
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/// <param name="length">待选项目的索引长度</param>
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/// <param name="select">输出项目的索引长度</param>
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/// <returns></returns>
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public static List<int> FisherYatesShuffle(int length, int select)
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{
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if(select > length)
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throw new ArgumentOutOfRangeException("在进行洗牌时，要求输出的项目比拥有的项目更多，这是不合理的。");
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var random = new System.Random();
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List<int> arr = Enumerable.Range(0, length).ToList();
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List<int> res = new List<int>();
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for(int i = 0; i < select; ++i)
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{
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int k = random.Next(arr.Count);
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res.Add(arr[k]);
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arr.RemoveAt(k);
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}
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return res;
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}
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/// <summary>
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/// 蓄水池抽样算法，可以在线程安全的情况下完成洗牌。
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/// </summary>
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/// <param name="arr"></param>
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/// <param name="select">需要抽取的样本 M</param>
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/// <param name="reservoir"></param>
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/// <param name="cancellationToken"></param>
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public static void ReservoirSampling(List<int> arr, int select, ConcurrentBag<int> reservoir, CancellationToken cancellationToken)
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{
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/**
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* int M = 3; // 需要抽样的元素个数
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* int totalElements = 10; // 输入数据的总元素个数
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* var arr = new List<int>();
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*
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* for (int i = 1; i <= totalElements; i++)
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* {
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* arr.Add(i);
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* }
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*
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* ConcurrentBag<int> reservoir = new ConcurrentBag<int>();
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* Random random = new Random();
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*
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* var cancellationTokenSource = new CancellationTokenSource();
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* var cancellationToken = cancellationTokenSource.Token;
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*
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* ThreadPool.QueueUserWorkItem(state =>
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* ReservoirSampling(arr, M, reservoir, random, cancellationToken);
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* , null);
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*
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* // 停止抽样
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* cancellationTokenSource.Cancel();
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*/
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var random = new System.Random();
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for(int i = select; i < arr.Count; ++i)
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{
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if(cancellationToken.IsCancellationRequested)
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return;
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int k = random.Next(i + 1); // 生成一个随机数 k，范围是 [0, i]
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if(k < select)
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{
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// 如果 k 小于 M，将 arr[k] 添加到抽样结果中
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reservoir.Add(arr[k]);
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}
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}
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}
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#endregion
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#region 应用算法
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/// <summary>
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/// 获取列表中随机顺序的对象
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <param name="list"></param>
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/// <param name="count">需要采样的数量</param>
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/// <returns></returns>
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public static IEnumerable<T> GetRandom<T>(this List<T> list, int count = -1)
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{
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var index = FisherYatesShuffle(list.Count, count <= 0 ? list.Count : count);
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for(int i = 0; i < index.Count; i++)
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yield return list[index[i]];
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}
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#endregion
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}
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} |