LeetCode 2 - Add Two Numbers ( JAVA )

Difficulity : 

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

/** * 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) {      ListNode prev = new ListNode(0);      ListNode head = prev;      int carry = 0;       while (l1 != null || l2 != null || carry != 0) {          ListNode cur = new ListNode(0);          int sum = ((l2 == null) ? 0 : l2.val) + ((l1 == null) ? 0 : l1.val) + carry;          cur.val = sum % 10;          carry = sum / 10;          prev.next = cur;  //使下以个指针指向cur          prev = prev.next;   //移动一个指针          l1 = (l1 == null) ? l1 : l1.next;          l2 = (l2 == null) ? l2 : l2.next;       }    return head.next;    }};

总结：效率比较高，对本题的理解可以画内存图，head和prev同时指向一个内存空间，之后移动prev指针指向下一个。head链表在不断的加长。