add-two-numbers.cc

// Add Two Numbers
class Solution {
public:
  ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
    ListNode *r = NULL, *p = NULL;
    int c = 0;
    while (l1 || l2) {
      if (l1) {
        c += l1->val;
        l1 = l1->next;
      }
      if (l2) {
        c += l2->val;
        l2 = l2->next;
      }
      auto x = new ListNode(c%10);
      c /= 10;
      if (! r)
        r = p = x;
      else {
        p->next = x;
        p = p->next;
      }
    }
    if (c)
      p->next = new ListNode(c);
    return r;
  }
};