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/**

* Practiced on 11/19/2012

*

* You are given two linked lists representing two non-negative numbers.

* The digits are stored in reverse order and each of their nodes contain a single digit.

* Add the two numbers and return it as a linked list.

* Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

* Output: 7 -> 0 -> 8

*/

package com.congli.leetcode;

public class AddTwoNumbers {

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

if(l1 == null && l2 == null) return null;

if(l1 == null) return l2;

if(l2 == null) return l1;

ListNode result = new ListNode(0);

ListNode runner = result;

int[] carry = {0};

while(l1 != null || l2 != null)

{

if(l1 != null && l2 != null)

{

runner.val = addHelper(l1.val, l2.val, carry);

l1 = l1.next;

l2 = l2.next;

}

else if(l1 != null)

{

runner.val = addHelper(l1.val, 0, carry);

l1 = l1.next;

}

else

{

runner.val = addHelper(l2.val, 0, carry);

l2 = l2.next;

}

if(l1 != null || l2 != null)

{

runner.next = new ListNode(0);

runner = runner.next;

}

}

if(carry[0] == 1) runner.next = new ListNode(1);

return result;

}

private int addHelper(int a, int b, int[] carry)

{

int result = a + b + carry[0];

carry[0] = result / 10;

return result % 10;

}

}