链表归并排序
真是恶心的一道题啊，哇了好多次才过。
代码：
1 void mergeList(ListNode *a, ListNode *b, ListNode *&h, ListNode *&t) { 2 h = t = NULL; 3 while (a && b) { 4 ListNode *c = NULL; 5 if (a->val <= b->val) { 6 c = a; 7 a = a->next; 8 } 9 else { 10 c = b; 11 b = b->next; 12 } 13 if (!h) 14 h = t = c; 15 else { 16 t->next = c; 17 t = t->next; 18 } 19 } 20 while (a) { 21 t->next = a; 22 t = t->next; 23 a = a->next; 24 } 25 while (b) { 26 t->next = b; 27 t = t->next; 28 b = b->next; 29 } 30 } 31 32 ListNode *sortList(ListNode *head) { 33 ListNode *prev = NULL; 34 ListNode *h1 = NULL; 35 ListNode *h2 = NULL; 36 ListNode *t1 = NULL; 37 ListNode *t2 = NULL; 38 ListNode *node = NULL; 39 int len = 0; 40 41 node = head; 42 while (node && (++len)) 43 node = node->next; 44 45 for (int l = 1; l < len; l <<= 1) { 46 prev = NULL; 47 h1 = NULL; 48 h2 = NULL; 49 t1 = NULL; 50 t2 = NULL; 51 node = head; 52 53 while (node) { 54 h1 = t1 = node; 55 for (int i = 0; node && i < l; i++) { 56 t1 = node; 57 node = node->next; 58 } 59 if (t1) 60 t1->next = NULL; 61 h2 = t2 = node; 62 for (int i = 0; node && i < l; i++) { 63 t2 = node; 64 node = node->next; 65 } 66 if (t2) 67 t2->next = NULL; 68 69 ListNode *h, *t; 70 if (h2) 71 mergeList(h1, h2, h, t); 72 else { 73 h = h1; 74 t = t1; 75 } 76 if (!prev) 77 head = h; 78 else 79 prev->next = h; 80 t->next = node; 81 prev = t; 82 } 83 } 84 85 return head; 86 }