leetcode笔记

语言：java

第二题

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

关键点： 相加进位，不定长度

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int next=0;
        ListNode r= new ListNode(0);
        ListNode nextPt= r;
        ListNode tl1=l1;
        ListNode tl2=l2;
        while(tl1!=null||tl2!=null){
           int val1=tl1!=null?tl1.val:0;
           int val2=tl2!=null?tl2.val:0;
            int sum=val1+val2+nextPt.val;
            nextPt.val=sum%10;
            if(sum>9){
                next=1;
            }
            if(tl1!=null)
                tl1=tl1.next;
            if(tl2!=null)
                tl2=tl2.next;
                
            if(tl1==null&&tl2==null&&next==0){
                nextPt.next=null;
            }else{
                nextPt.next=new ListNode(next);
                next=0;
                nextPt=nextPt.next;
            }
            
        }
        return r;
    }
}