leetcode week6

You are given two non-empty linked lists representing two non-negative integers. 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.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

问题描述：给定两个非空链表表示两个非负整数。如上面所述。最后要得到一个链表，这个链表表示给定的两个非空链表的和。

解题思路：问题本身比较简单，但是要利用链表这一数据结构。一般来说使用链表应当添加虚拟头部以方便使用。这里还需要一个变量用以保存进位信息。

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {        int flag = 0;        ListNode* dhead = new ListNode(0);        ListNode* ptr = dhead;                while(l1!=NULL || l2!=NULL){            int val1=0;            int val2=0;            if(l1!=NULL){                val1 = l1->val;                l1 = l1->next;            }            if(l2!=NULL){                val2 = l2->val;                l2 = l2->next;            }            int temp = val1 + val2 + flag;            ptr->next = new ListNode(temp % 10);            ptr = ptr->next;            flag = temp / 10;        }        if(flag==1){            ptr->next = new ListNode(1);        }        return dhead->next;    }};