letcode刷题之两数相加

letcode里面刷题，坑还是链表不熟，（1）头结点还是有必要设置，否则返回的时候找不到位置；（2）先设置next到新节点再next到下一个节点；都是基础知识

/*

 *

 * 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

 * */

class CONF{

	public static final int initialVal=-1;

}

class ListNode {

      int val=CONF.initialVal;

      ListNode next=null;

      ListNode(int x) { val = x; }

      ListNode(){};

}

public class addTwoNumber {

    public ListNode add(ListNode l1, ListNode l2) {

    	ListNode resHeadNode = new ListNode();

    	ListNode leftNode = l1.next,rightNode = l2.next,resNode=resHeadNode;

    	int addon=0;

    	while(leftNode!=null){

    	    ListNode tmpNode=new ListNode((leftNode.val+rightNode.val)%10+addon);

    		addon=(leftNode.val+rightNode.val)/10;

    	    resNode.next=tmpNode;

    	    resNode=resNode.next;

    		leftNode = leftNode.next;

    		rightNode= rightNode.next;

    	}

    	return resHeadNode;

    }

    public void initList(String[] vals,ListNode headList){

    	ListNode valList=headList;

    	for(int i=0;i<vals.length;i++){

    		ListNode tmpnode=new ListNode(Integer.valueOf(vals[i]));

    		valList.next=tmpnode;

    		valList=valList.next;

    	}

    }

    public static void printList(ListNode headList){

    	ListNode resNode=headList.next;

    	while(resNode!=null){

    		System.out.println("res:"+resNode.val);

    		resNode = resNode.next;

    	}

    }

    public static void main(String[] args){

    	addTwoNumber instance =new addTwoNumber();

    	ListNode leftList=new ListNode();

    	ListNode rightList=new ListNode();

    	instance.initList(new String[]{"2","4","3"},leftList);

    	instance.initList(new String[]{"5","6","4"},rightList);

    	System.out.println("leftList:");

    	printList(leftList);

    	System.out.println("rightList:");

    	printList(rightList);

    	ListNode resNodeList=instance.add(leftList,rightList);

    	System.out.println("resNodeList:");

    	printList(resNodeList);

    }

}