用归并法进行单链表排序 

  1 struct ListNode {
  2     int val;
  3     ListNode *next;
  4     ListNode(int x) : val(x), next(nullptr) {}
  5 };
  6 
  7 ListNode* median(ListNode *head)
  8 {
  9     if(head != nullptr && head->next != nullptr)
 10     {
 11         ListNode *m = head;
 12         ListNode *last = m->next;
 13         while(last->next != nullptr)
 14         {
 15             if((last = last->next) != nullptr) last = last->next;
 16             else break;
 17             m = m->next;
 18         }
 19         return m;
 20     }
 21     else return head;
 22 }
 23 
 24 ListNode* advance_aux(ListNode *head, int len)
 25 {
 26     while(--len > 0) head = head->next;
 27     return head;
 28 }
 29 
 30 ListNode** merge_aux(ListNode **l_head, ListNode **r_head, int l_len, int r_len)
 31 {
 32     cout<<"merge "
 33         <<(*l_head)->val<<' '<<l_len<<" and "
 34         <<(*r_head)->val<<' '<<r_len<<'\n';
 35     ListNode **left = l_head, **right = r_head;
 36     while(l_len != 0 && r_len != 0)
 37     {
 38         while(r_len != 0 && (*right)->val < (*left)->val)
 39         {
 40             right = &(*right)->next;
 41             --r_len;
 42         }
 43         if(*right == *r_head)
 44         {
 45             while(l_len != 0 && (*left)->val <= (*right)->val)
 46             {
 47                 left = &(*left)->next;
 48                 --l_len;
 49             }
 50         }
 51         else
 52         {
 53             cout<<"\tmove ["
 54                 <<(*r_head)->val<<","
 55                 <<(r_len ? (*right)->val : -1)
 56                 <<") before "
 57                 <<(*left)->val<<"\n";
 58             ListNode *tmp = *left;
 59             *left = *r_head;
 60             *r_head = *right;
 61             *right = tmp;
 62             left = &tmp->next;
 63             --l_len;
 64             right = r_head;
 65         }
 66     }
 67     while(r_len-- != 0)
 68     {
 69         ListNode *tmp = *left;
 70         *left = *r_head;
 71         *r_head = *right;
 72         *right = tmp;
 73     }
 74     return l_head;
 75 }
 76 
 77 ListNode** insertionSortList_aux(ListNode **head, int len)
 78 {
 79     cout<<"deal "<<(*head)->val<<' '<<len<<'\n';
 80     if(len > 2)
 81     {
 82         int left_len = len/2, right_len = len - left_len;
 83         head = insertionSortList_aux(head, left_len);
 84         ListNode *left_last = advance_aux(*head, left_len);
 85         ListNode **right_head = insertionSortList_aux(&left_last->next, right_len);
 86         head = merge_aux(head, right_head, left_len, right_len);
 87     }
 88     else if(len == 2)
 89     {
 90         if((*head)->val > (*head)->next->val)
 91         {
 92             int tmp = (*head)->val;
 93             (*head)->val = (*head)->next->val;
 94             (*head)->next->val = tmp;
 95         }
 96     }
 97     return head;
 98 }
 99 
100 ListNode* insertionSortList(ListNode *head)
101 {
102     int len = 0;
103     ListNode *last = head;
104     while(last != nullptr)
105     {
106         ++len;
107         last = last->next;
108     }
109     insertionSortList_aux(&head, len);
110     return head;
111 }
112 
113 ListNode* insertNode(ListNode *head, int i)
114 {
115     auto p = new ListNode{i};
116     p->next = head;
117     return p;
118 }
119 
120 int main()
121 {
122     ListNode *p = nullptr;
123     p = insertNode(p, 0);
124     p = insertNode(p, 0);
125     p = insertNode(p, 0);
126     p = insertNode(p, 0);
127     for(ListNode *i = p; i != nullptr; i = i->next) cout<<i->val<<" ";
128     cout<<endl;
129     p = insertionSortList(p);
130     for(ListNode *i = p; i != nullptr; i = i->next) cout<<i->val<<" ";
131     cout<<endl;
132     while(p != nullptr)
133     {
134         ListNode *tmp = p->next;
135         delete p;
136         p = tmp;
137     }
138 }

 

posted @ 2018-03-30 18:21  杨文的博客  阅读(297)  评论(0)    收藏  举报