快速排序

示意图如下：

下标0暂存i,不参与排序

代码如下：

#include<iostream>
//#include<string>

using namespace std;

int partition(int arr[], int begin_index, int end_index)
{
	int key = arr[end_index];
	int i = begin_index-1;
	for (int j = begin_index; j <= end_index - 1; j++)
	{
		if (arr[j] <= key)
		{
			i = i + 1;
			int t = arr[i];
			arr[i] = arr[j];
			arr[j] = t;
		}
		
	}
	int T = arr[i + 1];
	arr[i + 1] = arr[end_index];
	arr[end_index] = T;

	return i+1;
}

void quick_sort(int arr[], int begin_index, int end_index)
{
	if (begin_index < end_index)
	{
		int midle = partition(arr, begin_index, end_index);
		quick_sort(arr, begin_index, midle - 1);
		quick_sort(arr, midle + 1, end_index);
	}
}

void main()
{
	int arr1[] = {0, 2, 3, 5, 1, 4, 11, 6, 4, 8, 7 };
	const int arr_num = sizeof(arr1) / sizeof(int);
	for (int i = 1; i <arr_num; i++)
		cout << arr1[i] << " ";
	cout << endl;

	quick_sort(arr1, 1, arr_num-1);
	for (int i = 1; i < sizeof(arr1) / sizeof(int); i++)
		cout << arr1[i] << " ";
	cout << endl;
	system("pause");
}

随机化版本：

#include<iostream>
//#include<string>

using namespace std;

int partition(int arr[], int begin_index, int end_index)
{
	int key = arr[end_index];
	int i = begin_index-1;
	for (int j = begin_index; j <= end_index - 1; j++)
	{
		if (arr[j] <= key)
		{
			i = i + 1;
			int t = arr[i];
			arr[i] = arr[j];
			arr[j] = t;
		}
		
	}
	int T = arr[i + 1];
	arr[i + 1] = arr[end_index];
	arr[end_index] = T;

	return i+1;
}

int randomized_partition(int arr[], int begin_index, int end_index)
{
	int k = begin_index + rand() % (end_index - begin_index + 1);
	int t = arr[k];
	arr[k] = arr[end_index];
	arr[end_index] = t;
	return partition(arr, begin_index, end_index);
}
void quick_sort(int arr[], int begin_index, int end_index)
{
	if (begin_index < end_index)
	{
		int midle = randomized_partition(arr, begin_index, end_index);
		quick_sort(arr, begin_index, midle - 1);
		quick_sort(arr, midle + 1, end_index);
	}
}

void main()
{
	int arr1[] = {0, 2, 3, 5, 1, 4, 11, 6, 4, 8, 7 };
	const int arr_num = sizeof(arr1) / sizeof(int);
	for (int i = 1; i <arr_num; i++)
		cout << arr1[i] << " ";
	cout << endl;

	quick_sort(arr1, 1, arr_num-1);
	for (int i = 1; i < sizeof(arr1) / sizeof(int); i++)
		cout << arr1[i] << " ";
	cout << endl;
	system("pause");
}