2. Add Two Numbers

Add Two Numbers

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

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1.解题思路

由于数字是逆序排列，所以分别从l1和l2中获取节点，计算val的和，将进位保存在add中。

/** * 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) {        ListNode l=null,p=null,q=null;        int add = 0;        int sum;        while(l1!=null && l2!=null){            sum= l1.val+l2.val+add;            add = sum/10;            sum = sum%10;            q = new ListNode(sum);            if(l==null){                l = q;                p = l;            }else{                p.next = q;                p = p.next;            }            l1 = l1.next;            l2 = l2.next;        }        while(l1!=null){            sum = l1.val + add;            add = sum/10;            sum = sum%10;            l1.val = sum;            p.next = l1;            l1 = l1.next;            p = p.next;            p.next = null;        }        while(l2!=null){            sum = l2.val + add;            add = sum/10;            sum = sum%10;            l2.val = sum;            p.next = l2;            l2 = l2.next;            p = p.next;            p.next = null;        }        if(add!=0){            q = new ListNode(add);            p.next = q;        }        return l;    }}