LeetCode #2 Add Two Numbers (M)

標籤：

[Problem]

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

 

[Analysis]

這題的思路比較簡單，只需要把兩個ListNode相加可能出現的四種情況列清楚：

1. L1 != null && L2 != null 

2. L1 != null && L2 == null 

3. L1 ==? null && L2 != null 

4. ?L1 == L2 == null && carry == 1

 

[Solution] 

public class Solution {        public ListNode addTwoNumbers(ListNode l1, ListNode l2) {        ListNode currentNode = new ListNode(0);                return addTwoNumbers(l1, l2, currentNode, 0).next;    }        public ListNode addTwoNumbers(ListNode l1, ListNode l2, ListNode currentNode, int carry) {        int val1 = 0;        int val2 = 0;                if (l1 != null) {            val1 = l1.val;            l1 = l1.next;                        if (l2 != null) {                val2 = l2.val;                l2 = l2.next;            }         } else {            if (l2 != null) {                val2 = l2.val;                l2 = l2.next;            } else {                if (carry != 0) {                    currentNode.next = new ListNode(carry);                                    }                                return currentNode;            }        }                int val = val1 + val2 + carry;                        ListNode newNode = new ListNode(val % 10);        currentNode.next = addTwoNumbers(l1, l2, newNode, val/10);                        return currentNode;    }}

 

LeetCode #2 Add Two Numbers (M)