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;

     }