Leetcode#148 Sort List

原题地址

链表归并排序

真是恶心的一道题啊，哇了好多次才过。

代码：

 void mergeList(ListNode *a, ListNode *b, ListNode *&h, ListNode *&t) {
   h = t = NULL;
   while (a && b) {
     ListNode *c = NULL;
     if (a->val <= b->val) {
       c = a;
       a = a->next;
     }
     else {
       c = b;
       b = b->next;
     }
     if (!h)
       h = t = c;
     else {
       t->next = c;
       t = t->next;
     }
   }
   while (a) {
     t->next = a;
     t = t->next;
     a = a->next;
   }
   while (b) {
     t->next = b;
     t = t->next;
     b = b->next;
   }
 }

 ListNode *sortList(ListNode *head) {
   ListNode *prev = NULL;
   ListNode *h1 = NULL;
   ListNode *h2 = NULL;
   ListNode *t1 = NULL;
   ListNode *t2 = NULL;
   ListNode *node = NULL;
   int len = ;

   node = head;
   while (node && (++len))
     node = node->next;

   for (int l = ; l < len; l <<= ) {
     prev = NULL;
     h1 = NULL;
     h2 = NULL;
     t1 = NULL;
     t2 = NULL;
     node = head;

     while (node) {
       h1 = t1 = node;
       for (int i = ; node && i < l; i++) {
         t1 = node;
         node = node->next;
       }
       if (t1)
         t1->next = NULL;
       h2 = t2 = node;
       for (int i = ; node && i < l; i++) {
         t2 = node;
         node = node->next;
       }
       if (t2)
         t2->next = NULL;

       ListNode *h, *t;
       if (h2)
         mergeList(h1, h2, h, t);
       else {
         h = h1;
         t = t1;
       }
       if (!prev)
         head = h;
       else
         prev->next = h;
       t->next = node;
       prev = t;
     }
   }

   return head;
 }