Comment on page

445.Add-Two-Numbers-II

445. Add Two Numbers II

题目地址

题目描述

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first 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.
​
Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
​
Example:
​
Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 8 -> 0 -> 7

代码

Approach #1 Two Stack

/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
Stack<Integer> s1 = new Stack<Integer>();
Stack<Integer> s2 = new Stack<Integer>();
​
while (l1 != null) {
s1.push(l1.val);
l1 = l1.next;
}
​
while (l2 != null) {
s2.push(l2.val);
l2 = l2.next;
}
​
int sum = 0;
ListNode head = new ListNode(0);
while (!s1.empty() || !s2.empty()) {
if (!s1.empty()) sum += s1.pop();
if (!s2.empty()) sum += s2.pop();
head.val = sum % 10;
ListNode node = new ListNode(sum / 10);
node.next = head;
head = node;
sum /= 10;
}
​
return head.val == 0 ? head.next : head;
}
}