# 445. Add Two Numbers II

## Description

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Input: l1 = [7,2,4,3], l2 = [5,6,4]
Output: [7,8,0,7]


Example 2:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [8,0,7]


Example 3:

Input: l1 = [0], l2 = [0]
Output: [0]


Constraints:

• The number of nodes in each linked list is in the range [1, 100].
• 0 <= Node.val <= 9
• It is guaranteed that the list represents a number that does not have leading zeros.

Follow up: Could you solve it without reversing the input lists?

## Solutions

• /**
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode() {}
*     ListNode(int val) { this.val = val; }
*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
Deque<Integer> s1 = new ArrayDeque<>();
Deque<Integer> s2 = new ArrayDeque<>();
for (; l1 != null; l1 = l1.next) {
s1.push(l1.val);
}
for (; l2 != null; l2 = l2.next) {
s2.push(l2.val);
}
ListNode dummy = new ListNode();
int carry = 0;
while (!s1.isEmpty() || !s2.isEmpty() || carry != 0) {
int s = (s1.isEmpty() ? 0 : s1.pop()) + (s2.isEmpty() ? 0 : s2.pop()) + carry;
// ListNode node = new ListNode(s % 10, dummy.next);
// dummy.next = node;
dummy.next = new ListNode(s % 10, dummy.next);
carry = s / 10;
}
return dummy.next;
}
}

• /**
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode() : val(0), next(nullptr) {}
*     ListNode(int x) : val(x), next(nullptr) {}
*     ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
stack<int> s1;
stack<int> s2;
for (; l1; l1 = l1->next) s1.push(l1->val);
for (; l2; l2 = l2->next) s2.push(l2->val);
ListNode* dummy = new ListNode();
int carry = 0;
while (!s1.empty() || !s2.empty() || carry) {
int s = carry;
if (!s1.empty()) {
s += s1.top();
s1.pop();
}
if (!s2.empty()) {
s += s2.top();
s2.pop();
}
// ListNode* node = new ListNode(s % 10, dummy->next);
// dummy->next = node;
dummy->next = new ListNode(s % 10, dummy->next);
carry = s / 10;
}
return dummy->next;
}
};

• # Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
self, l1: Optional[ListNode], l2: Optional[ListNode]
) -> Optional[ListNode]:
s1, s2 = [], []
while l1:
s1.append(l1.val)
l1 = l1.next
while l2:
s2.append(l2.val)
l2 = l2.next
dummy = ListNode()
carry = 0
while s1 or s2 or carry:
s = (0 if not s1 else s1.pop()) + (0 if not s2 else s2.pop()) + carry
carry, val = divmod(s, 10)
# node = ListNode(val, dummy.next)
# dummy.next = node
dummy.next = ListNode(val, dummy.next)
return dummy.next


• /**
* type ListNode struct {
*     Val int
*     Next *ListNode
* }
*/
func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
s1, s2 := arraystack.New(), arraystack.New()
for l1 != nil {
s1.Push(l1.Val)
l1 = l1.Next
}
for l2 != nil {
s2.Push(l2.Val)
l2 = l2.Next
}
carry, dummy := 0, new(ListNode)
for !s1.Empty() || !s2.Empty() || carry > 0 {
s := carry
v, ok := s1.Pop()
if ok {
s += v.(int)
}
v, ok = s2.Pop()
if ok {
s += v.(int)
}
// node := &ListNode{s % 10, dummy.Next}
// dummy.Next = node
dummy.Next = &ListNode{s % 10, dummy.Next}
carry = s / 10
}
return dummy.Next
}

• /**
* class ListNode {
*     val: number
*     next: ListNode | null
*     constructor(val?: number, next?: ListNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.next = (next===undefined ? null : next)
*     }
* }
*/

function addTwoNumbers(l1: ListNode | null, l2: ListNode | null): ListNode | null {
const s1: number[] = [];
const s2: number[] = [];
for (; l1; l1 = l1.next) {
s1.push(l1.val);
}
for (; l2; l2 = l2.next) {
s2.push(l2.val);
}
const dummy = new ListNode();
let carry = 0;
while (s1.length || s2.length || carry) {
const s = (s1.pop() ?? 0) + (s2.pop() ?? 0) + carry;
// const node = new ListNode(s % 10, dummy.next);
// dummy.next = node;
dummy.next = new ListNode(s % 10, dummy.next);
carry = Math.floor(s / 10);
}
return dummy.next;
}


• // Definition for singly-linked list.
// #[derive(PartialEq, Eq, Clone, Debug)]
// pub struct ListNode {
//   pub val: i32,
//   pub next: Option<Box<ListNode>>
// }
//
// impl ListNode {
//   #[inline]
//   fn new(val: i32) -> Self {
//     ListNode {
//       next: None,
//       val
//     }
//   }
// }
impl Solution {
fn create_stack(mut head: Option<Box<ListNode>>) -> Vec<i32> {
let mut res = vec![];
while let Some(node) = head {
res.push(node.val);
}
res
}

l1: Option<Box<ListNode>>,
l2: Option<Box<ListNode>>
) -> Option<Box<ListNode>> {
let mut s1 = Self::create_stack(l1);
let mut s2 = Self::create_stack(l2);

let mut dummy = Box::new(ListNode::new(0));
let mut carry = 0;
while !s1.is_empty() || !s2.is_empty() || carry != 0 {
if let Some(val) = s1.pop() {
carry += val;
}
if let Some(val) = s2.pop() {
carry += val;
}
dummy.next = Some(
Box::new(ListNode {
val: carry % 10,
next: dummy.next.take(),
})
);
carry /= 10;
}
dummy.next.take()
}
}