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
Tag : dummy node
/**
* 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) {
if(l1 == null && l2 == null) {
return null;
}
if(l1 == null) {
return l2;
}
if(l2 == null) {
return l1;
}
ListNode head = new ListNode(0);
ListNode dummy = head;
int carry = 0;
while(l1 != null && l2 != null) {
int val = (l1.val + l2.val + carry) % 10;
carry = (l1.val + l2.val + carry) / 10;
ListNode node = new ListNode(val);
head.next = node;
head = node;
l1 = l1.next;
l2 = l2.next;
}
while(l1 != null) {
int val = (l1.val + carry) % 10;
carry = (l1.val + carry) / 10;
ListNode node = new ListNode(val);
head.next = node;
head = node;
l1 = l1.next;
}
while(l2 != null) {
int val = (l2.val + carry) % 10;
carry = (l2.val + carry) / 10;
ListNode node = new ListNode(val);
head.next = node;
head = node;
l2 = l2.next;
}
if(carry != 0) {
ListNode node = new ListNode(carry);
head.next = node;
}
return dummy.next;
}
}
leetcode 最佳参考解法：
public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
ListNode c1 = l1;
ListNode c2 = l2;
ListNode sentinel = new ListNode(0);
ListNode d = sentinel;
int sum = 0;
while (c1 != null || c2 != null) {
sum /= 10;
if (c1 != null) {
sum += c1.val;
c1 = c1.next;
}
if (c2 != null) {
sum += c2.val;
c2 = c2.next;
}
d.next = new ListNode(sum % 10);
d = d.next;
}
if (sum / 10 == 1)
d.next = new ListNode(1);
return sentinel.next;
}
}
leetcode : Add two numbers 解题报告
原文：http://www.cnblogs.com/superzhaochao/p/6358608.html