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;
    }