給你兩個 非空 的鏈表，表示兩個非負的整數(shù)。它們每位數(shù)字都是按照 逆序 的方式存儲的，并且每個節(jié)點只能存儲 一位 數(shù)字。

請你將兩個數(shù)相加，并以相同形式返回一個表示和的鏈表。

你可以假設除了數(shù)字 0 之外，這兩個數(shù)都不會以 0 開頭。

/**

?*?Definition?for?singly-linked?list.

?*?public?class?ListNode?{

?*?????int?val;

?*?????ListNode?next;

?*?????ListNode()?{}

?*?????ListNode(int?val)?{?this.val?=?val;?}

?*?????ListNode(int?val,?ListNode?next)?{?this.val?=?val;?this.next?=?next;?}

?*?}

?*/

class?Solution?{

????public?ListNode?addTwoNumbers(ListNode?l1,?ListNode?l2)?{

????????

????????//?Initialize?variables

????????ListNode?result?=?new?ListNode(0);?//?Head?node

????????ListNode?prevNode?=?result;

????????int?carry?=?0;

????????

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

????????????int?x?=?(l1?!=?null)???l1.val?:?0;

????????????int?y?=?(l2?!=?null)???l2.val?:?0;

????????????int?sum?=?x?+?y?+?carry;

????????????

????????????//?Update?carry

????????????if?(sum?>?9)?{

????????????????carry?=?1;

????????????????sum?%=?10;

????????????}?else?{

????????????????carry?=?0;

????????????}

????????????

????????????//?Update?the?linked?list

????????????ListNode?currentNode?=?new?ListNode(sum);

????????????prevNode.next?=?currentNode;

????????????prevNode?=?currentNode;

????????????

????????????//?Move?to?the?next?nodes?of?l1?and?l2

????????????if?(l1?!=?null)?{

????????????????l1?=?l1.next;

????????????}

????????????if?(l2?!=?null)?{

????????????????l2?=?l2.next;

????????????}

????????}

????????//?Check?if?there?is?any?carry?left

????????if?(carry?!=?0)?{

????????????prevNode.next?=?new?ListNode(carry);

????????}

????????

????????//?Return?the?resulting?list

????????return?result.next;

????}

}