LeetCode题解之Add two numbers

1、题目描述

2、题目描述

题目思路可以参考合并单链表的思路，定义一个全局 进位标志，如果两个数值相加得到需要进位，则将进位标志置为1 。

3、代码

  ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
 
         ListNode* head = new ListNode(  ) ;
         ListNode* result = head;
         ListNode* p1 = l1;
         ListNode* p2 = l2;
         int up  = ;
         while( p1 != NULL && p2 != NULL )
         {
             int r = p1->val + p2->val ;
              r += up;
             if( r <  )
             {
                 result->next = new ListNode( r ) ;
                 up = ;
             }
             else
             {
                 result -> next = new ListNode( r -) ;
                 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 !=   && p1 == NULL && p2 == NULL )
         {
             result->next = new ListNode(up) ;
         }
         return head->next;
 
     }