[Sword means offer] 16. Merge two sorted lists

"Idea 1" recursion

1 /*2 struct ListNode {3 int val;4 struct ListNode *next;5 listnode (int x):6 val (x), Next (NULL) {7     }8 };*/9 classSolution {Ten  Public: Onelistnode* Merge (listnode* pHead1, listnode*pHead2) A     { -         if(PHead1 = =NULL) -             returnpHead2; the         Else if(PHead2 = =NULL) -             returnPHead1; -listnode* res =NULL; -         if(Phead1->val <= phead2->val) { +res =PHead1; -Res->next = Merge (phead1->Next, pHead2); +}Else{ Ares =pHead2; atRes->next = Merge (phead1,phead2->next); -         } -         returnRes; -     } -};

"Train of Thought 2" non-recursive, create a new list and save the head node, the original two linked list to be compared sequentially inserted into the new linked list, and finally will have the remaining linked list directly connected.

1 /*2 struct ListNode {3 int val;4 struct ListNode *next;5 listnode (int x):6 val (x), Next (NULL) {7     }8 };*/9 classSolution {Ten  Public: Onelistnode* Merge (listnode* pHead1, listnode*pHead2) { A         if(PHead1 = =NULL) -             returnpHead2; -         Else if(PHead2 = =NULL) the             returnPHead1; -listnode* res =NULL; -listnode* cur =NULL; -          while(PHead1! = NULL && pHead2! =NULL) { +             if(Phead1->val <= phead2->val) { -                 if(res = =NULL) +res = cur =PHead1; A                 Else{ atCur->next =PHead1; -Cur = cur->Next; -                 } -PHead1 = phead1->Next; -}Else{ -                 if(res = =NULL) inres = cur =pHead2; -                 Else{ toCur->next =pHead2; +Cur = cur->Next; -                 } thePHead2 = phead2->Next; *             } $         }Panax Notoginseng         if(PHead1 = =NULL) { -Cur->next =pHead2; the         } +         if(PHead2 = =NULL) { ACur->next =PHead1; the         } +         returnRes; -     } $};

[Sword means offer] 16. Merge two sorted lists