链表实现两个数字相加

两个用链表表示的数字相加

https://leetcode.com/problems/add-two-numbers/

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

从头开始加，若后面不够需要新建链表结点。

若想方便可以不断新建结点保存每位的和，若要时间复杂度底，就直接加在某个链表上。

此处演示加在某个链表上的代码

public ListNode addTwoNumbers(ListNode l1, ListNode l2){
if(l1 == null) return l2;
else if(l2 == null) return l1;
else{
ListNode ls1 = l1, ls2 = l2;
int sum = 0, prog = 0;
while(ls1 != null && ls2 != null){
sum = ls1.val + ls2.val+ prog;
ls1.val = sum%10;
prog = sum/10;
if(ls1.next == null || ls2.next == null) break;
ls1 = ls1.next;
ls2 = ls2.next;
}
if(ls1.next == null) ls1.next = ls2.next;
while(prog != 0){
if(ls1.next == null) {
ls1.next = new ListNode(prog);
prog = 0;
}
else{
ls1 = ls1.next;
sum = ls1.val + prog;
ls1.val = sum%10;
prog = sum/10;
}
}
}
return l1;
}