Leetcode2. Add Two Numbers

题目：

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

思路：

没啥思路，就一位一位对应加就行，注意进位。

代码写得比较渣，但是好理解，也AC了。

import java.util.LinkedList;class ListNode {    int val;    ListNode next;    ListNode(int x) { val = x; }}public class Test {    public static ListNode addTwoNumbers(ListNode l1, ListNode l2) {        int carry = 0;        LinkedList<Integer> list = new LinkedList();        while(l1 != null && l2 != null) {            int a = l1.val;            int b = l2.val;            int result = a + b + carry;            if(result >= 10) {                result %= 10;                carry = 1;            }else {                carry = 0;            }            list.add(result);            l1 = l1.next;            l2 = l2.next;        }        while(l1 != null) {            int result = l1.val + carry;            if(result >= 10) {                result %= 10;                carry = 1;            }else {                carry = 0;            }            list.add(result);            l1 = l1.next;        }        while(l2 != null) {            int result = l2.val + carry;            if(result >= 10) {                result %= 10;                carry = 1;            }else {                carry = 0;            }            list.add(result);            l2 = l2.next;        }        if(carry != 0) {            list.add(carry);        }        // 创造返回链表        ListNode head = new ListNode(list.removeFirst());        ListNode result = head;        while(!list.isEmpty()) {            head.next = new ListNode(list.removeFirst());            head = head.next;        }        return result;    }    public static ListNode createTestCase(int[] arr) {        ListNode head = new ListNode(-1);        ListNode h = head;        for(int i = 0; i < arr.length; i++) {            head.next = new ListNode(arr[i]);            head = head.next;        }        return h.next;    }    public static void print(ListNode head) {        while(head != null) {            System.out.print(head.val + " ");            head = head.next;        }        System.out.println();    }    public static void main(String[] args) {        // Test case        int[] arr1 = {2,4,5,1};        int[] arr2 = {5,6,4};        ListNode l1 = createTestCase(arr1);        ListNode l2 = createTestCase(arr2);        ListNode l3 = addTwoNumbers(l1, l2);        print(l3);    }}