快速排序的多种思路实现：
两边想中间靠拢：
// 两边想中间靠拢，当a[left]<key a[right]>key时，两者交换
int PartSortBothSize(int *a, int left, int right)
{
assert(a != NULL);
int key = a[right];
int begin = left;
int end = right - 1;
while (begin < end)
{
while (begin<end && (a[begin]<=key))
{
++begin;
}
while (begin<end&&(a[end]>=key))
{
--end;
}
if (begin < end)
{
swap(a[begin], a[end]);
}
}
if (a[begin]>a[right])
{
swap(a[begin], a[right]);
return begin;
}
return right;
}挖坑法：
// 挖坑法left right是坑 a[left]>key 时 将a[left]放到right位置，a[right]<key时，将a[right]放到left位置
int PartSortPotholing(int *a, int left, int right)
{
assert(a != NULL);
int key = a[right];
int begin = left;
int end = right;
while (left<right)
{
while (left<right&&a[left] <= key)
{
left++;
}
if (left < right)
{
a[right] = a[left];
right--;
}
while (left<right&&a[right] >= key)
{
right--;
}
if (left < right)
{
a[left] = a[right];
left++;
}
}
a[left] = key;
return left;
}顺向
//顺向
//left、right从左向右走，当a[left]<key时，left停止，当a[right]>key,right停止，交换两者对应的值
int PartSortBothRight(int *a, int left, int right)
{
assert(a != NULL);
int key = a[right];
int prev = left;
while (a[left] < key)//当开始的数字比key小移动left、prev
{
left++; prev++;
}
while (left < right)
{
while (left < right&&a[left] >= key)
{
left++;
}
while (left < right&&a[prev] <= key)
{
prev++;
}
if (left < right)
{
swap(a[left], a[prev]);
left++; prev++;
}
}
swap(a[prev], a[left]);
return prev;
}调用函数：
void _QuickSort(int *a, int left,int right)
{
assert(a != NULL);
if (left >= right)
{
return;
}
//int div = PartSortBothSize(a, left, right);
//int div = PartSortPotholing(a, left, right);
int div = PartSortBothRight(a, left, right);
if (div > 0)
{
_QuickSort(a, left, div - 1);
}
if (div < right - 1)
{
_QuickSort(a, div + 1, right);
}
}
void QuickSort(int *a, size_t size)
{
assert(a != NULL);
if (size > 1)
{
_QuickSort(a, 0, size - 1);
}
}test:
int a4[] = { 0, 5, 2, 1, 5, 5, 7, 8, 5, 6, 9, 4, 3, 5, -2, -4, -1 };
原文地址：http://10739786.blog.51cto.com/10729786/1776031
