topN 堆排序 （int 类型）
2012-06-26 15:00 yuejianjun 阅读(399) 评论(0) 编辑 收藏 举报using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
namespace Test
{
class Program
{
static void Main(string[] args)
{
List<int> testValues = new List<int>();
Random rand = new Random();
int count = 100;
for (int i = 0; i < count; i++)
{
testValues.Add(rand.Next());
}
int[] testArr = new int[testValues.Count];
testValues.CopyTo(testArr);
Stopwatch sw = new Stopwatch();
sw.Reset();
sw.Start();
TopSort(testArr, 5);
sw.Stop();
Console.WriteLine(count+" 耗时毫秒："+sw.ElapsedMilliseconds);
Console.Read();
}
public static void TopSort(int [] array, int top )
{
//Judge input
if (array.Length <= 2 || top >= array.Length / 2)
{
Array.Sort(array);
return;
}
//One time partition
int pivot = PartitionInt(array, 0, array.Length - 1, array.Length / 2);
int lastPivot = pivot;
//Run until pivot near the top
while ((!(lastPivot >= top && pivot <= top)))
{
lastPivot = pivot;
if (pivot > top)
{
pivot = PartitionInt(array, 0, pivot, pivot / 2);
if (pivot == lastPivot)
{
pivot--;
}
}
else
{
if (pivot >= array.Length - 1)
{
lastPivot = array.Length - 1;
break;
}
pivot = PartitionInt(array, pivot + 1, array.Length - 1, (array.Length - pivot) / 2);
}
}
//Finally sort
if (lastPivot < array.Length)
{
Array.Sort(array, 0, lastPivot + 1);
}
else
{
Array.Sort(array, 0, lastPivot);
}
}
private static int PartitionInt(int[] array, int low, int high, int pivotIndex)
{
int pivotValue = array[pivotIndex];
array[pivotIndex] = array[low];
array[low] = pivotValue;
while (low < high)
{
while (array[high] >= pivotValue && high > low)
{
--high;
}
if (high > low)
{
array[low] = array[high];
}
while (array[low] <= pivotValue && high > low)
{
++low;
}
if (high > low)
{
array[high] = array[low];
}
}
array[low] = pivotValue;
return low;
}
}
}
