快速排序(快排)算法的C++两种实现

快排算法在分治的时候有两种实现，一种实现是从两边到中间(partition)，另一种实现是从一边到另一边(partition2)。我用一个100000数组测试发现前一种实现运行速度快一些。

这两种的C++实现如下： （注：我用的代码风格是gnu的代码风格）

bool sort::qsort(int *ini, int start, int end)
{ // sort the array ini by ascending order
int tmp=0;
int mid=0;

if (end < start){
return false;
}else if(end == start){
if(ini[start] > ini[end])
{
tmp = ini[start];
ini[start] = ini[end];
ini[end] = tmp;
}
return true;
}else{			   // when start is less end;
mid = this->partition2(ini, start, end);
// the partition fun. can either be partiton or partiton2.

if(mid == start && qsort(ini,mid+1,end))
return true;

if( mid == end && qsort(ini,start,mid-1))
return true;

if(qsort(ini,start,mid-1) && qsort(ini,mid+1,end))
return true;
return true;
}
}

int sort::partition(int *ini, int start, int end)
{   // the main body for partition which from edge to middle
int key=0;
int i=start;
int j=end;
int tmp = 0;
key = ini[i];

while(i!=j)
{
while(key <= ini[j] && i < j)
j--;

// exchange value, from right to left
tmp = ini[i];
ini[i] = ini[j];
ini[j] = tmp;

while(key >= ini[i] && i < j)
i++;

// exchange value, from left to right
tmp = ini[i];
ini[i] = ini[j];
ini[j] = tmp;
}

return i;
}

int sort::partition2(int *ini, int start, int end)
{   // the main body for partition which from end to begin
int key = ini[end];
int i = start - 1;		// suppose the mid pos is i+1
int j=start;
int tmp = 0;

for(;j<end;j++)
{
if(ini[j] < key )
{
i++;
tmp = ini[i];
ini[i] = ini[j];
ini[j] = tmp;
}
}
ini[end] = ini[i+1];
ini[i+1] = key;
return i+1;
}