两种快速排序算法性能的比较

先来看看第一种快速排序算法（QuickSort1）：

#include <iostream>
#include <fstream>
#include <ctime>

#define MAXNUM 1024

using namespace std;

void QuickSort(int A[], int low, int high)
{
	if(low>=high)
		return;
	int first = low;
	int last = high;
	int key = A[first];	//用第一个元素做主元
	while(first<last)
	{
		while(first<last && A[last]>=key)
			--last;
		A[first] = A[last];	//把比key小的元素换到主元前面
		while(first<last && A[first]<=key)
			++first;
		A[last] = A[first];	//把比key大的元素换到主元后面

	}
	A[first] = key;	//确定一个元素(主元)的最终位置
	QuickSort(A, low, first-1);		//比key小的前半部分元素继续进行快排
	QuickSort(A, first+1, high);	//比key大的后半部分元素继续进行快排
}

int main()
{
	clock_t t1, t2;
	t1 = clock();

	int A[MAXNUM];
	int size=0;
	int i=0;
	fstream in("data.txt");
	if(!in)
		cout << "Open error!" << endl;
	while(!in.eof())
	{
		in >> A[i];
		++i;
	}
	size = i-1;
	in.close();
	QuickSort(A, 0, size-1);
	
	for(i=0; i<size; i++)
		cout << A[i] << " ";
	cout << endl;

	t2 = clock();
	cout << "TIME: " << (double)(t2-t1)/CLOCKS_PER_SEC << endl;
	return 0;
}

#include <iostream>
#include <fstream>
#include <ctime>

#define MAXNUM 8000

using namespace std;

//对数组A[]进行就地重排
int Partition(int A[], int p, int r)
{
	int x = A[r];		//主元
	int i = p-1;		//不大于主元x的元素下标都不大于i
	for(int j=p; j<=r-1; ++j)
	{
		if(A[j]<=x)
		{
			i++;
			swap(A[i], A[j]);
		}
	}
	swap(A[i+1], A[r]);
	return (i+1);
}

//快速排序算法
void QuickSort(int A[], int p, int r)
{
	int q;
	if(p < r)
	{
		q = Partition(A, p, r);
		QuickSort(A, p, q-1);
		QuickSort(A, q+1, r);
	}
}

int main()
{
	clock_t t1, t2;
	t1 = clock();

	int A[MAXNUM];
	int i=0;
	int size = 0;
	fstream in("data.txt");
	if(!in)
		cout << "Open error!" << endl;
	while(!in.eof())
	{
		in >> A[i];
		++i;
	}
	size = i-1;
	in.close();
	QuickSort(A, 0, size-1);
	
	for(i=0; i<size; ++i)
		cout << A[i] << " ";
	cout << endl;

	t2 = clock();
	cout << "TIME: " << static_cast<double>(t2-t1)/CLOCKS_PER_SEC << endl;
	return 0;
}