《Cracking the Coding Interview》——第2章：链表——题目4

2014-03-18 02:27

题目：将一个单链表按照一个值X分为两部分，小于X的部分放在大于等于X的部分之前。

解法：按照值和X的大小，分链表为两条链表，然后连起来成一条。

代码：

 1 // 2.4 Write code to partition a linked list around a value x, such that all nodes less than x comes before all nodes greater than or equal to x.

 2 #include <cstdio>

 3 using namespace std;

 4 

 5 struct ListNode {

 6     int val;

 7     ListNode *next;

 8     ListNode(int x): val(x), next(nullptr) {};

 9 };

10 

11 class Solution {

12 public:

13     ListNode* partitionList(ListNode *head, int x) {

14         if (head == nullptr) {

15             return head;

16         }

17         

18         ListNode *h1, *t1, *h2, *t2;

19         ListNode *ptr;

20         

21         h1 = t1 = nullptr;

22         h2 = t2 = nullptr;

23         ptr = head;

24         while (ptr != nullptr) {

25             if (ptr->val < x) {

26                 if (h1 == nullptr) {

27                     h1 = t1 = ptr;

28                 } else {

29                     t1->next = ptr;

30                     t1 = t1->next;

31                 }

32                 ptr = ptr->next;

33                 t1->next = nullptr;

34             } else {

35                 if (h2 == nullptr) {

36                     h2 = t2 = ptr;

37                 } else {

38                     t2->next = ptr;

39                     t2 = t2->next;

40                 }

41                 ptr = ptr->next;

42                 t2->next = nullptr;

43             }

44         }

45         if (h1 == nullptr) {

46             return h2;

47         } else if (h2 == nullptr) {

48             return h1;

49         } else {

50             t1->next = h2;

51             return h1;

52         }

53     }

54 };

55 

56 int main()

57 {

58     int i;

59     int n, x;

60     int val;

61     struct ListNode *head, *ptr;

62     Solution sol;

63     

64     while (scanf("%d", &n) == 1 && n > 0) {

65         // create a linked list

66         ptr = head = nullptr;

67         for (i = 0; i < n; ++i) {

68             scanf("%d", &val);

69             if (head == nullptr) {

70                 head = ptr = new ListNode(val);

71             } else {

72                 ptr->next = new ListNode(val);

73                 ptr = ptr->next;

74             }

75         }

76         

77         // partition the list around value x.

78         scanf("%d", &x);

79         head = sol.partitionList(head, x);

80         

81         // print the list

82         printf("%d", head->val);

83         ptr = head->next;

84         while (ptr != nullptr) {

85             printf("->%d", ptr->val);

86             ptr = ptr->next;

87         }

88         printf("\n");

89         

90         // delete the list

91         while (head != nullptr) {

92             ptr = head->next;

93             delete head;

94             head = ptr;

95         }

96     }

97     

98     return 0;

99 }