Add Two Numbers (Java)

LeetCode

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

Solution: use two references point to the head of each list and add them and carry one by one. 

	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
	/**
	* Definition for singly-linked list.
	* public class ListNode {
	* int val;
	* ListNode next;
	* ListNode(int x) {
	* val = x;
	* next = null;
	* }
	* }
	*/
	public class AddTwoNumbers {
	public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
	if (l1==null){
	return l2;
	}
	if (l2==null){
	return l1;
	}
	ListNode preHead=new ListNode(-1);
	ListNode end=preHead;
	ListNode node1=l1;
	ListNode node2=l2;
	int carry=0;
	while(node1!=null || node2!=null ||carry!=0){
	int current=0;
	if (node1!=null){
	current+=node1.val;
	node1=node1.next;
	}
	if (node2!=null){
	current+=node2.val;
	node2=node2.next;
	}
	if (carry!=0){
	current+=carry;
	}
	end.next=new ListNode(current%10);
	end=end.next;
	carry=current/10;
	}
	return preHead.next;
	}
	}

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