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：

 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 }