Add Two Numbers LeetCode solution in C++

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class Solution {
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 public:
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  ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
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    ListNode *dummy = new ListNode(0);
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    ListNode *curr = dummy;
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    int carry = 0;
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    while (l1 != NULL || l2 != NULL || carry == 1) {
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      int sum = 0;
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      if (l1 != NULL) {
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        sum += l1->val;
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        l1 = l1->next;
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      }
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      if (l2 != NULL) {
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        sum += l2->val;
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        l2 = l2->next;
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      }
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      sum += carry;
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      carry = sum / 10;
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      ListNode *node = new ListNode(sum % 10);
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      curr->next = node;
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      curr = curr->next;
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    }
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    return dummy->next;
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  }
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};