/*

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.

Example

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

Output: 7 -> 0 -> 8

*/

public class AddTwoLinkedLists {

class ListNode {

public int value;

public ListNode next;

public ListNode(int value) {

this.value = value;

next = null;

}

}

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

// Write your solution here

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

return l2;

}

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

return l1;

}

ListNode dummy = new ListNode(0);

ListNode cur = dummy;

int sum = 0;

int carry = 0;

while(l1 != null && l2 != null) {

sum = l1.value + l2.value + carry;

carry = sum / 10; // !!!! should calculate first

if(carry > 0) {

sum = sum % 10;

}

ListNode newNode = new ListNode(sum);

cur.next = newNode;

cur = cur.next;

l1 = l1.next;

l2 = l2.next;

}

while(l2 != null) { // should keep while loop to add all nodes left

sum = l2.value + carry;

carry = sum / 10;

if(carry > 0) {

sum = sum % 10;

}

ListNode newNode = new ListNode(sum);

cur.next = newNode;

cur = cur.next;

l2 = l2.next;

}

while(l1 != null) {

sum = l1.value + carry;

carry = sum / 10;

if(carry > 0) {

sum = sum % 10;

}

ListNode newNode = new ListNode(sum);

cur.next = newNode;

cur = cur.next;

l1 = l1.next;

}

if(carry != 0) { // !!!! there maybe carry left and need to be added

ListNode newNode = new ListNode(carry);

cur.next = newNode;

}

return dummy.next;

}

}