LeetCode 题解之Add Two Numbers II

1、题目描述

2、分析

首先将链表翻转，然后做加法。

最后将结果链表翻转。

3、代码

 ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {

         ListNode* L1 = reverseList( l1 );
         ListNode* L2 = reverseList( l2 );

         ListNode*  head = new ListNode(  );
         ListNode* result = head;
         ListNode* p1 = L1;
         ListNode* p2  = L2;
         int up = ;
         while( p1 != NULL && p2 != NULL )
         {
             if( p1->val + p2->val + up <  )
             {
                 result->next = new ListNode( p1->val + p2->val + up );
                 up = ;
             }else{
                 result->next = new ListNode( p1->val + p2->val + up -  );
                 up = ;
             }
             p1 = p1->next;
             p2 = p2->next;
             result = result->next;
         }

         while( p1 != NULL )
         {
             if( p1->val + up <  )
             {
                 result->next = new ListNode( p1->val + up );
                 up = ;
             }
             else
             {
                 result->next = new ListNode( p1->val + up -  );
                 up = ;
             }
             p1 = p1->next;
             result = result->next;
         }

         while( p2 != NULL )
         {
             if( p2->val + up <   )
             {
                 result->next  = new ListNode( p2->val + up );
                 up = ;
             }
             else
             {
                 result->next = new ListNode( p2->val + up -  );
                 up = ;
             }
             p2 = p2->next;
             result = result ->next;
         }

         if( up ==  )
         {
             result->next = new ListNode();
             result = result->next;
         }
         ListNode* re = reverseList( head->next ) ;
         return re;

     }

     ListNode* reverseList(ListNode* l)
     {
         ListNode* p1 = l;
         ListNode*  p2 = l->next;
         while( p2 != NULL )
         {
             ListNode* tmp = p2->next;
             p2 ->next = p1;
             p1 = p2;
             p2 = tmp;
         }

         l->next = NULL ;
         return p1;
     }