Add Two Numbers II 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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    ListNode res = new ListNode(0);
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    ListNode curr = res;
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    l1 = reverseLinkedList(l1);
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    l2 = reverseLinkedList(l2);
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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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      curr.next = new ListNode(sum % 10);
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      curr = curr.next;
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    }
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    return reverseLinkedList(res.next);
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  }
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  public ListNode reverseLinkedList(ListNode head) {
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    ListNode curr = head;
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    ListNode prev = null;
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    ListNode next;
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    while (curr != null) {
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      next = curr.next;
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      curr.next = prev;
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      prev = curr;
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      curr = next;
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    }
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    return prev;
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  }
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}