快排的两种写法

快排方法一：

附：全代码实现

#include<iostream>
#include<assert.h>
using namespace std;

int OnceSort(int *a, int left, int right)
{
	int i = 0;
	int middle = right;
	right -= 1;

	while (left < right)
	{
		//left找大于middle的数
		while (left < right && *(a + left) <= *(a + middle))
			left++;

		//right找小于middle的数
		while (left < right && *(a + right) > *(a + middle))
			right--;

		if (left < right)
		{
			swap(*(a + left), *(a + right));
		}
		else
		{
			break;
		}
	}
	if (*(a + left) < *(a + middle))
	{
		i = left + 1;
	}
	else
	{
		i = left;
	}
	while (i < middle)
	{
		swap(*(a + middle - 1), *(a + middle));
		middle--;
	}
	return i;
}

void QuickSort(int* a, int left, int right)
{
	assert(a);
	int middle = 0;
	if (left < right)
	{
		middle = OnceSort(a, left, right);
		QuickSort(a, left, middle - 1);
		QuickSort(a, middle + 1, right);
	}
}

int main()
{
//	int a[] = { 6, 5, 4, 1, 4, 2, 4, 3 };
	int a[] = { 9, 9, 9, 7, 7, 7, 8, 8, 8, 3, 2, 1, 8, 6 };
	QuickSort(a, 0, sizeof(a) / sizeof(a[0]) - 1);
	return 0;
}

快排方法二：

代码实现，下附：

#include<iostream>
using namespace std;

int onceSort(int a[], int left, int right)
{
	int key = a[left];
	while (left < right)
	{
		while (left < right && (*(a + right) >= key))
		{
			right--;
		}
		if (left < right && (*(a + right) < key))
			swap(*(a + right), *(a + left));
		while (left < right && (*(a + left) < key))
		{
			left++;
		}
		if (left < right && (*(a + left) >= key))
			swap(*(a + left), *(a + right));
	}
	a[left] = key;
	return left;
}

void QuickSort(int a[], int left, int right)
{
	int middle = 0;
	if (left < right)
	{
		middle = onceSort(a, left, right);
		QuickSort(a, left, middle - 1);
		QuickSort(a, middle + 1, right);
	}
}

int main()
{
	int a[] = {2,1,4,3,8,7,5,6,4,4,4,4,4};
	QuickSort(a, 0, sizeof(a) / sizeof(a[0]) - 1);
	return 0;
}

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