LeetCode题解之Merge Two Sorted Lists

1、题目描述

2、题目分析

题目要求合并有序的两个链表，要求不能额外申请空间。

3、代码

 1 ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
 2         if( l1 == NULL )return l2;
 3         if( l2 == NULL )return l1;
 4         if( l1 == NULL && l2 == NULL ) return NULL;
 5         ListNode* r = ( l1->val <= l2->val )?l1:l2; 
 6         if( l1->val <= l2->val ){
 7             l1 = l1->next;
 8         }else{
 9             l2 =  l2->next;
10         }
11             
12         ListNode* pm = r ;  
13         while( l1 != NULL && l2 != NULL ){
14            if( l1->val <= l2->val ){
15                pm->next = l1;
16                l1 = l1->next;
17            }else{
18                pm->next = l2;
19                l2 = l2->next;
20            }
21             pm = pm->next;
22         }
23         
24         if( l1 != NULL ){
25             pm->next = l1;
26         }
27         if( l2 != NULL ){
28             pm->next = l2;
29         }
30         
31         return r;
32     }