10亿个数中找出1000个最大的数的算法思路：
1，先拿出前1000个数字，并排序，找出最小值为 minValue .
2, 然后再依次拿出1000个数字，找出最大值为 tempMaxValue.
3, 如果tempMaxValue 比 minValue 大， 则将 theMaxValue 放入前1000个数中,再排序并找出minValue .
4 .. 依此类推。 即可得到1000个最大的数。
以下是本人测试的代码 。可以参考，欢迎高手指正，谢谢！
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;
namespace test
{
public class Class1
{
private const int MaxLength = 100000000;
private const int EachCount = 1000;
public static void TestDirectSort()
{
Console.WriteLine(" test start :" + DateTime.Now.ToLongTimeString());
int[] orignList = new int[MaxLength];
Random rd = new Random();
for (int i = 0; i < MaxLength; i++)
{
orignList[i] = rd.Next();
}
ArrayList list = new ArrayList(MaxLength);
list.AddRange(orignList);
list.Sort();
int[] retList = new int[1000];
int j = 0;
for (int i = MaxLength - 1; i > MaxLength - 1000; i++)
{
retList[j] = orignList[i];
j++;
}
Console.WriteLine(" test end : " + DateTime.Now.ToLongTimeString());
foreach (int i in list)
{
Console.WriteLine(i.ToString());
}
Console.WriteLine("end: " + DateTime.Now.ToLongTimeString());
}
public static void TestSort()
{
Console.WriteLine(" test start :" + DateTime.Now.ToLongTimeString());
int[] orignList = new int[MaxLength] ;
Random rd = new Random();
for (int i = 0; i < MaxLength; i++)
{
orignList[i] = rd.Next();
}
ArrayList foreList = new ArrayList();
if (MaxLength > EachCount)
{
for (int i = 0; i < EachCount; i++)
{
foreList.Add(orignList[i]);
}
foreList.Sort();
int addValue = EachCount;
for (int j = 1; j < MaxLength / EachCount +1 ; j++)
{
ArrayList tempList = new ArrayList();
for (int k = j * addValue; k < j * addValue + EachCount; k++)
{
if (k >= MaxLength) break;
//tempList[k - j * addValue] = orignList[k];
tempList.Add(orignList[k]);
}
tempList.Sort();
for (int m = tempList.Count -1; m >=0 ; m--)
{
if ((int)tempList[m] <= (int)foreList[0])
break;
foreList[0] = tempList[m];
foreList.Sort();
}
}
}
else
{
foreList.AddRange(orignList);
foreList.Sort();
}
Console.WriteLine(" test end : " + DateTime.Now.ToLongTimeString());
foreach (int i in foreList)
{
Console.WriteLine(i.ToString());
}
Console.WriteLine("end: " + DateTime.Now.ToLongTimeString());
}
}
public class client
{
public static void Main()
{
Class1.TestSort();
// Class1.TestDirectSort();
Console.Read();
}
}
}