AddTwoNumbers.java

package leetcode;

import util.ListNode;

/**
 * Created by nikoo28 on 7/5/19 12:29 AM
 */

class AddTwoNumbers {

  public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    if (l1 == null)
      return l2;

    if (l2 == null)
      return l1;

    ListNode l3 = null;
    ListNode ans = null;

    int carry = 0;
    while (l1 != null || l2 != null) {

      int x, y;
      x = l1 == null ? 0 : l1.val;
      y = l2 == null ? 0 : l2.val;

      int val = x + y + carry;
      carry = 0;

      if (val >= 10) {
        carry = 1;
        val = val % 10;
      }

      if (ans == null) {
        l3 = new ListNode(val);
        ans = l3;
      } else {
        l3.next = new ListNode(val);
        l3 = l3.next;
      }

      if (l1 != null) l1 = l1.next;
      if (l2 != null) l2 = l2.next;
    }

    if (carry == 1) {
      l3.next = new ListNode(1);
    }

    return ans;
  }

}