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//快速排序，C实现
//2014年 07月 30日 星期三 23:59:52 CST
#include <iostream>
#include <cassert>
using namespace std;
//交换两个变量的值
void swap(int *a, int *b)
{
int temp = *a;
*a = *b;
*b = temp;
}
//快速排序划分算法
//思路：选取最后一个元素作为基准元素pivot，指定两个游标i,j
// j指示所有处理过元素的边界, i指示所有小于pivot的边界
// 然后j从前之后扫描数组
// 如果比基准元素小,则递增i，同时交换i,j所知元素
int partition(int *arr, int start, int end)
{
int pivot, i, j;
pivot = arr[end];
i = start - 1;
for (j = start; j < end; ++j)
{
if (arr[j] <= pivot)
{
++i;
swap(&arr[i], &arr[j]);
}
}
swap(&arr[i+1], &arr[end]);
return i + 1;
}
int partition2(int *arr, int start, int end)
{
int pivot = arr[start];
int low, high;
low = start;
high = end;
while(low < high)
{
while(low < high && arr[high] > pivot)
--high;
arr[low] = arr[high];
while(low < high && arr[low] < pivot)
++low;
arr[high] = arr[low];
}
arr[low] = pivot;
return low;
}
//注意调用quick_sort_core的实参+1/-1，遗漏可能导致死循环
void quick_sort_core(int *arr, int start, int end)
{
if (start < end)
{
int pivot_num = partition2(arr, start, end);
quick_sort_core(arr, start, pivot_num - 1);
quick_sort_core(arr, pivot_num + 1, end);
}
}
void quick_sort(int *arr, int n)
{
assert(arr != NULL && n > 0);
quick_sort_core(arr, 0, n - 1);
}
void print_array(int *arr, int n)
{
assert(arr != NULL && n > 0);
for (int i = 0; i < n; ++i)
cout << *(arr + i) << "\t";
cout << endl;
}
int main()
{
int aArray[] = { 6, 8, 3, 2, 7, 1, 5};
int n = sizeof(aArray) / sizeof(int);
cout << "数组排序前所有元素为:" << endl;
print_array(aArray, n);
quick_sort(aArray, n);
cout << "数组快速排序后所有元素为:" << endl;
print_array(aArray, n);
return 0;
}