sort-list--linked list, fast and slow pointer to find the middle, merge sort

Sort a linked list in O(n log n) time using constant space complexity.

Linked list, fast and slow pointer to find the midpoint, merge sort.

Pay attention to judging condition fast->next!=null&&fast->next->next!=null, if fast!=null&&fast->next!= Null will cause a memory overflow

1 /**2 * Definition for singly-linked list.3 * struct ListNode {4 * int val;5 * ListNode *next;6 * ListNode (int x): Val (x), Next (NULL) {}7  * };8  */9 classSolution {Ten  Public: OneListNode *sortlist (ListNode *head) { A         if(Head==null | | head->next==NULL) -             returnhead; -listnode* Slow, *fast; theslow=head; -fast=head; -          while(fast->next!=null&&fast->next->next!=NULL) { -Slow=slow->Next; +Fast=fast->next->Next; -         } +fast=slow; ASlow=slow->Next; atfast->next=NULL; -fast=Sortlist (head); -slow=sortlist (slow); -         returnmerge (Fast,slow); -          -     } inListNode *merge (ListNode *left, ListNode *Right ) { -ListNode *res,*temp; to         if(left==NULL) { +res=Right ; -             returnRes; the         } *         if(right==NULL) { $res=Left ;Panax Notoginseng             returnRes; -         } the         if(left->val<=right->val) { +res=Left ; ALeft=left->Next; the}Else{ +res=Right ; -Right=right->Next; $         } $temp=Res; -          while(left!=null&&right!=NULL) { -             if(left->val<=right->val) { thetemp->next=Left ; -Left=left->Next;Wuyi}Else{ thetemp->next=Right ; -Right=right->Next; Wu             } -Temp=temp->Next; About              $         } -         if(left!=NULL) { -temp->next=Left ; -         } A         if(right!=NULL) { +temp->next=Right ; the         } -         returnRes; $     } the};

sort-list--linked list, fast and slow pointer to find the middle, merge sort