Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

题意：合并两个已排序的链表

题不难，但是有很多需要注意的细节，直接贴代码

1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     struct ListNode *next; 6  * }; 7  */ 8 struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) { 9     struct ListNode *tmp,*p1,*p2;10     if(l1==NULL){11         tmp=l1;12         l1=l2;13         l2=tmp;14     }15     if(l1==NULL)16         return l1;17     p1=l1;18     p2=l2;19     while(l1!=NULL){20         if(l2!=NULL&&l1->val<=l2->val){21             while(l1->next!=NULL&&l1->next->val<=l2->val) 22                 l1=l1->next;23             tmp=l2;24             l2=l2->next;25             tmp->next=l1->next;26             l1->next=tmp;27             l1=l1->next;28         }29         else if(l2!=NULL&&l1->val>l2->val){30             tmp=l1;31             l1=l2;32             l2=tmp;33             p1=l1;34         }35         else if(l2==NULL)36             return p1;37     }38     return p1;39 }

 感觉写的好乱，重新写一遍：

1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     struct ListNode *next; 6  * }; 7  */ 8 struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) { 9     struct ListNode *tmp,*p1;10     if(l1==NULL&&l2==NULL)11         return NULL;12     if(l1==NULL)13         return l2;14     if(l2==NULL)15         return l1;16     if(l1->val>l2->val){17         tmp=l1;18         l1=l2;19         l2=tmp;20     }21     p1=l1;22     while(l1!=NULL){23         if(l2!=NULL&&l1->val<=l2->val){24             while(l1->next!=NULL&&l1->next->val<=l2->val) 25                 l1=l1->next;26             tmp=l2;27             l2=l2->next;28             tmp->next=l1->next;29             l1->next=tmp;30         }31         else if(l2==NULL)32             return p1;33     }34     return p1;35 }