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

 ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
         if( l1 == NULL )return l2;
         if( l2 == NULL )return l1;
         if( l1 == NULL && l2 == NULL ) return NULL;
         ListNode* r = ( l1->val <= l2->val )?l1:l2;
         if( l1->val <= l2->val ){
             l1 = l1->next;
         }else{
             l2 =  l2->next;
         }

         ListNode* pm = r ;
         while( l1 != NULL && l2 != NULL ){
            if( l1->val <= l2->val ){
                pm->next = l1;
                l1 = l1->next;
            }else{
                pm->next = l2;
                l2 = l2->next;
            }
             pm = pm->next;
         }

         if( l1 != NULL ){
             pm->next = l1;
         }
         if( l2 != NULL ){
             pm->next = l2;
         }

         return r;
     }