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);
    }
}