【JAVA、C++】LeetCode 002 Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

解题思路：

定义三个ListNode l1、l2，result，其中result为return语句的输出，l1、l2为传入的参数。

将l1赋值给result，执行result.val+=l2.val，然后l1作为指针一级一级往下走，直到走到l2.next为null。当然，之间会有不少边界条件，自己debug一下就好。

Java代码如下：

public class Solution {
      static public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    	ListNode result=l1;
    	while(true){
    		l1.val+=l2.val;
    		if(l1.val>=10){
    			l1.val%=10;
    			if(l1.next==null) l1.next=new ListNode(1);
    			else l1.next.val+=1;
    		}

		if(l2.next==null){
			ListNode l3=l1.next;
			while(true){
				if (l3==null) break;
				if(l3.val==10){
					l3.val%=10;
	    			if(l3.next==null) l3.next=new ListNode(1);
	    			else l3.next.val+=1;
				}
				l3=l3.next;
			}
			break;
		}

    	l2=l2.next;
    	if(l1.next==null){
    		l1.next=new ListNode(0);
    	}
    	l1=l1.next;
    	}
    	return result;

    }
}

C++

 class Solution {
 public:
     ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
         ListNode* res=l1;
         while (true) {
             l1->val += l2->val;
             if (l1->val >= ) {
                 l1->val %= ;
                 if (l1->next == NULL)
                     l1->next = new ListNode();
                 else l1->next->val += ;
             }

             if (l2->next == NULL) {
                 ListNode* l3 = l1->next;
                 while (true) {
                     if (l3 == NULL) break;
                     if (l3->val == ) {
                         l3->val %= ;
                         if (l3->next == NULL) l3->next = new ListNode();
                         else l3->next->val += ;
                     }
                     l3 = l3->next;
                 }
                 break;
             }

             l2 = l2->next;
             if (l1->next == NULL) {
                 l1->next = new ListNode();
             }
             l1 = l1->next;
         }
         return res;
     }
 };