public class AddTwoNumbers {

/**

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

Output: 7 -> 0 -> 8

time : O(n)

space : O(n)

* @param l1

* @param l2

* @return

*/

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

ListNode dummy = new ListNode (0); // dummy in order to return from the beginning node

ListNode cur = dummy; // a pointer to traverse

int sum = 0;

ListNode p1 = l1, p2 = l2;

while(p1 != null || p2 != null){

if(p1 != null){

sum += p1.val;

p1 = p1.next;

}

if(p2 != null){

sum += p2.val;

p2 = p2.next;

}

cur.next = new ListNode(sum%10); //if sum < 10, if > 10 cur.next is the remainder.

sum /= 10; // if sum < 10, sum update to 0, else taking the carries 1.

cur = cur.next;

}

// if the last sum is > 10;

if(sum == 1){

cur.next = new ListNode(1);

}

return dummy.next;

}

public static void main(String[] args) {

System.out.println("sss");

}

}