如下，一組4元矢量的排序，如何把排序時間縮減一半？可以用並行算法。
using System;
using System.Collections.Generic;
using System.Diagnostics;
namespace Vector4Test
{
public class Vector
{
public double W;
public double X;
public double Y;
public double Z;
public double T;
}
internal class VectorComparer : IComparer<Vector>
{
public int Compare(Vector c1, Vector c2)
{
if (c1 == null || c2 == null)
throw new ArgumentNullException("Both objects must not be null");
double x = Math.Sqrt(Math.Pow(c1.X, 2)
+ Math.Pow(c1.Y, 2)
+ Math.Pow(c1.Z, 2)
+ Math.Pow(c1.W, 2));
double y = Math.Sqrt(Math.Pow(c2.X, 2)
+ Math.Pow(c2.Y, 2)
+ Math.Pow(c2.Z, 2)
+ Math.Pow(c2.W, 2));
if (x > y)
return 1;
else if (x < y)
return -1;
else
return 0;
}
}
internal class VectorComparer2 : IComparer<Vector> {
public int Compare(Vector c1, Vector c2) {
if (c1 == null || c2 == null)
throw new ArgumentNullException("Both objects must not be null");
if (c1.T > c2.T)
return 1;
else if (c1.T < c2.T)
return -1;
else
return 0;
}
}
internal class Program
{
private static void Main(string[] args)
{
Vector[] vectors = GetVectors();
var watch1 = new Stopwatch();
watch1.Start();
A(vectors);
watch1.Stop();
Console.WriteLine("A sort time: " + watch1.Elapsed);
vectors = GetVectors();
watch1.Reset();
watch1.Start();
B(vectors);
watch1.Stop();
Console.WriteLine("B sort time: " + watch1.Elapsed);
vectors = GetVectors();
watch1.Reset();
watch1.Start();
C(vectors);
watch1.Stop();
Console.WriteLine("C sort time: " + watch1.Elapsed);
Console.ReadKey();
}
private static Vector[] GetVectors()
{
int n = 1 << 15;
var vectors = new Vector[n];
var random = new Random();
for (int i = 0; i < n; i++)
{
vectors[i] = new Vector();
vectors[i].X = random.NextDouble();
vectors[i].Y = random.NextDouble();
vectors[i].Z = random.NextDouble();
vectors[i].W = random.NextDouble();
}
return vectors;
}
private static void A(Vector[] vectors)
{
Array.Sort(vectors, new VectorComparer());
}
private static void B(Vector[] vectors) {
int n = vectors.Length;
for (int i = 0; i < n; i++)
{
Vector c1 = vectors[i];
c1.T = Math.Sqrt(Math.Pow(c1.X, 2)
+ Math.Pow(c1.Y, 2)
+ Math.Pow(c1.Z, 2)
+ Math.Pow(c1.W, 2));
}
Array.Sort(vectors,new VectorComparer2());
}
private static void C(Vector[] vectors) {
int n = vectors.Length;
for (int i = 0; i < n; i++) {
Vector c1 = vectors[i];
c1.T = Math.Sqrt(c1.X * c1.X
+ c1.Y * c1.Y
+ c1.Z * c1.Z
+ c1.W * c1.W);
}
Array.Sort(vectors, new VectorComparer2());
}
}
}
我暈，剛開始我用的算法A，後來又寫了個算法B，我還沒用並行算法呢，一看B方法比A方法時間縮短了差不多兩個數量級，如下
A sort time: 00:00:00.5346475
B sort time: 00:00:00.0169736
太奇怪了也，難道我的B算法二級緩存命中率比較高？誰能再把我的B方法消耗時間再降低一半，可以用任何語言，Vector類等也可以用自己的數據類型，比如結構啦，四維數組啥的，隨意，只要是四元的矢量，每個分量是隨機生成的，然後每個矢量的長度是根號下每個分量的平方和，滿足這個條件就行。
modify by wawa at 2009-04-22 06:42
應大家回帖要求，
1、把隨機數種子初始的語句放到了循環外面
2、每次執行排序重新獲取新的亂序Vector
3、把B方法直接對計算出來的double[]排序換成了對對vector[]的排序，因為之前的代碼實際上沒有對vector[]排序
4、把Vector類增加了值T，用來保存該Vector的長度。
我這裡結果如下
A sort time: 00:00:00.6661531
B sort time: 00:00:00.0423115
C sort time: 00:00:00.0302426
