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

 1  ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
 2         
 3         ListNode* head = new ListNode( 0 ) ;
 4         ListNode* result = head;
 5         ListNode* p1 = l1;
 6         ListNode* p2 = l2;
 7         int up  = 0;
 8         while( p1 != NULL && p2 != NULL )
 9         {
10             int r = p1->val + p2->val ;
11              r += up;
12             if( r < 10 )
13             {
14                 result->next = new ListNode( r ) ;
15                 up = 0;
16             } 
17             else
18             {
19                 result -> next = new ListNode( r -10) ;
20                 up  = 1;
21             }
22             p1 = p1->next;
23             p2 = p2->next;
24             result = result ->next;
25         }
26         
27        
28         
29         while( p1 != NULL )
30         {
31            if( p1->val + up < 10 )
32            {
33                result->next = new ListNode( p1->val + up );
34                up = 0;
35            }else{
36                result->next = new ListNode( p1->val + up - 10 );
37                up = 1;
38            }
39             p1 = p1->next;
40             result = result ->next;
41         }
42         
43         while( p2 != NULL )
44         {
45             if(p2->val + up < 10) 
46             {
47                 result->next = new ListNode( p2->val + up);
48                 up = 0;
49             }
50             else
51             {
52                 result->next = new ListNode( p2->val + up - 10 ) ;
53                 up = 1;
54             }
55             p2 = p2->next;
56             result = result->next;
57         }
58         
59         if( up != 0  && p1 == NULL && p2 == NULL )
60         {
61             result->next = new ListNode(up) ;
62         }
63         return head->next;
64         
65     }