快排算法的实现

单链表的快排

void QuickSort(struct Node *head,struct Node *tail)
{
if(head == NULL)
return ;
if(head == tail )
return ;
int pivot = head->data;
struct Node *p = head;
struct Node *q = p->next;
while(q != tail)
{
if(q->data<pivot) //每次都选择待排序链表的头结点作为划分的基准
{
p = p->next;
int tmp = p->data; //p指针指向比基准小的节点组成的链表
p->data = q->data;
q->data =tmp;
}
q=q->next;
}
int tmp = p->data; 
p->data = head->data;
head->data =tmp;
QuickSort(head,p); //比基准元素小的链表
QuickSort(p->next,NULL); //右边是比基准大的节点组成的链表
}

快排的非递归实现

int Partition(int *a,int low,int high)
{
while(low<high)
{
while(low<high && a[high] >= a[low])
--high;
swap(a[low],a[high]);
while(low<high && a[low] <= a[high])
++low;
swap(a[low],a[high]);
}
return low;
}


void quickSort(int *a,int low ,int high) {
if(a== NULL || low< 0 || high <0)
return ;
stack<int> s;
if(low<high)
{
int pivot = Partition(a,low,high);
if(low < pivot -1)
{
s.push(low);
s.push(pivot-1);
}
if(pivot+1 < high)
{
s.push(pivot+1);
s.push(high);
}
while(!s.empty())
{
int start = s.top();
s.pop();
int end = s.top();
s.pop();
pivot = Partition(a,start,end);
if(start < pivot -1 )
{
s.push(start);
s.push(pivot-1);
}
if(pivot+1 < end)
{
s.push(pivot+1);
s.push(end);
} 
}
}
}