[.NET]產生不重覆的數值(List vs HashSet)

2013-05-30

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.NET
2013-05-31

在產生不重覆的數值時，可考慮使用HashSet，效能會比使用List來的好哦!

在網路上看到「Generate distinct random numbers in C#」，要產生不重覆的數值，可透過HashSet<int>來產生，會比List<int>來的快哦!

所以在這裡記錄一下。

環境: Win8 X64, Intel i7, 8G RAM, VS2012

如下，在0~50000之間取30000個不重覆的數值，

以下使用List<int>，花費時間為 3.3094352 秒


Random rand = new Random();
List<int> result = new List<int>();
const int minValue = 0;
const int maxValue = 50001;
// Create new stopwatch
Stopwatch stopwatch = new Stopwatch();

// Begin timing
stopwatch.Start();
for (Int32 i = 0; i < 30000; i++)
{
	int curValue = rand.Next(minValue, maxValue);
	while (result.Contains(curValue))
	{
		curValue = rand.Next(minValue, maxValue);
	}
	result.Add(curValue);
}
var resultArray = result.ToArray();
// Stop timing
stopwatch.Stop();

// Write result
Console.WriteLine("Time elapsed: {0}",
	stopwatch.Elapsed);

以下使用HashSet<int>，花費時間為 0.0155939 秒


Random rand = new Random();
HashSet<int> check = new HashSet<int>();
const int minValue = 0;
const int maxValue = 50001;
// Create new stopwatch
Stopwatch stopwatch = new Stopwatch();

// Begin timing
stopwatch.Start();
for (Int32 i = 0; i < 30000; i++)
{
	int curValue = rand.Next(minValue, maxValue);
	while (check.Contains(curValue))
	{
		curValue = rand.Next(minValue, maxValue);
	}
	check.Add(curValue);
}
var resultArray = check.ToArray();
// Stop timing
stopwatch.Stop();

// Write result
Console.WriteLine("Time elapsed: {0}",
	stopwatch.Elapsed);

感謝「Aaron」的提醒。