O(nlogn)时间复杂度 链表排序

int counter = 0;// statistic

struct list_node
{
int val;
struct list_node* next;
list_node(int t, struct list_node* pn = 0)
{
val = t;
next = pn;
}
};

typedef list_node* list;

void insert_list(list& h, int t)
{
if (0 == h)
{
h = new list_node(t);
return;
}

list pn = new list_node(t, h);
h = pn;
}

// find the middle node of the list
list find_mid(list h)
{
list pn = h;
if (0 == pn->next || 0 == pn) return pn;
while(h != 0 && h->next != 0)// && h->next->next != 0) // it is needless
{
pn = pn->next;
h = h->next->next;
}
return pn;
}

list merge_list(list h1, list h2)
{
list hret = (0 != h1) ? h1:h2;// head of the returned list
if (0 == hret) return hret;

hret = (h1->val < h2->val) ? h1:h2;
if (hret == h1)
h1 = h1->next;
else
h2 = h2->next;

list ret = hret; // the last node of the returned list
while( (0 != h1) && (0 != h2) )
{
counter ++;// no usage, just for statistic
if (h1->val < h2->val)
{
ret->next = h1;
ret = h1;// reassign ret
h1 = h1->next;
}
else
{
ret->next = h2;
ret = h2;// reassign ret
h2 = h2->next;
}
}

// attach the remained nodes to the ret list
if (0 != h1)	ret->next = h1;
else if(0 != h2)	ret->next = h2;
else ret->next = 0; // 0 is the end of the returned list

return hret;
}

list merge_sort_list(list h)
{
if (0==h ||0==h->next) return h;

list mid1 = find_mid(h);
if (0 == mid1) return 0;

list mid = mid1->next;
mid1->next = 0;// break up the list h into h and mid

list h1 = merge_sort_list(h);
list h2 = merge_sort_list(mid);

counter++;// no usage, just for statistic
return merge_list(h1, h2);
}

int main(int argc, char* argv[])
{
list h = 0;// necessary to initialize, else h1 equal to 0xcccccccc
for (int i=0 ;i< 4096; ++i)
insert_list(h, rand()%100000);

list ret = merge_sort_list(h);
cout<<counter<<endl;// show how many operations
while(0 != ret)
{
cout<<ret->val<<endl;
ret = ret->next;
}
return 0;
}