Add Two Numbers LeetCode solution in Java

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class Solution {
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  public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
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    if (l1 == null) return l2;
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    if (l2 == null) return l1;
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    ListNode dummy = new ListNode(-1);
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    ListNode temp = dummy;
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    int carry = 0;
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    while (l1 != null || l2 != null || carry != 0) {
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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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      temp.next = node;
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      temp = temp.next;
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    }
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    return dummy.next;
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  }
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}