src.cpp

#include <cstdio>
#include <cstdlib>
using namespace std;
struct ListNode {
     int val;
     ListNode *next;
     ListNode(int x) : val(x), next(NULL) {}
 };
class Solution {

public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
		ListNode *p = l1, *q = l2, *result = NULL, *last;
		int len1 = 0, len2 = 0;
		while (p && q) {
			len1++, len2++;
			p = p->next;
			q = q->next;
		}
		while(p) {
			len1++;
			p = p->next;
		}
		while (q) {
			len2++;
			q = q->next;
		}
		if (len1 >= len2) {
			p = l1;
			q = l2;
			result = l1;
		}
		else {
			p = l2;
			q = l1;
			result = l2;
		}
		bool carry = false;
		while (p && q) {
			p -> val = (p -> val + q -> val);
			if (carry)
				p -> val++;
			if (p->val >= 10) {
				p->val -= 10;
				carry = true;
			} else {
				carry = false;
			}
			last = p;
			p = p->next;
			q = q->next;
		}
		while (p && carry) {
			if (++(p->val) >= 10) {
				p->val -= 10;
			} else
				carry = false;
			last = p;
			p = p->next;
		}
		if (carry)
			last->next = new ListNode(1);
		return result;
    }
};
int main(int argc, char **argv)
{
	Solution solution;
	ListNode *l1 = new ListNode(5);
	ListNode *l2 = new ListNode(5);

	auto result = solution.addTwoNumbers(l1, l2);
	while (result) {
		printf("%d ", result->val);
		result = result -> next;
	}
	return 0;
}