Description
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 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 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.
Example 2:
Input: l1 = [0], l2 = [0]
Output: [0]
Example 3:
Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]
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.
Solutions
Solution 1: Simulation
We traverse two linked lists $l_1$ and $l_2$ at the same time, and use the variable $carry$ to indicate whether there is a carry.
Each time we traverse, we take out the current bit of the corresponding linked list, calculate the sum with the carry $carry$, and then update the value of the carry. Then we add the current bit to the answer linked list. If both linked lists are traversed, and the carry is $0$, the traversal ends.
Finally, we return the head node of the answer linked list.
The time complexity is $O(\max (m, n))$, where $m$ and $n$ are the lengths of the two linked lists. We need to traverse the entire position of the two linked lists, and each position only needs $O(1)$ time. Ignoring the space consumption of the answer, the space complexity is $O(1)$.
PythonJavaC++GoTypeScriptRustJavaScriptC#PHPSwiftRubyNimC
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def addTwoNumbers(
self, l1: Optional[ListNode], l2: Optional[ListNode]
) -> Optional[ListNode]:
dummy = ListNode()
carry, curr = 0, dummy
while l1 or l2 or carry:
s = (l1.val if l1 else 0) + (l2.val if l2 else 0) + carry
carry, val = divmod(s, 10)
curr.next = ListNode(val)
curr = curr.next
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
return dummy.next(code-box)
/**
* Definition for singly-linked list.
* 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) {
ListNode dummy = new ListNode(0);
int carry = 0;
ListNode cur = dummy;
while (l1 != null || l2 != null || carry != 0) {
int s = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + carry;
carry = s / 10;
cur.next = new ListNode(s % 10);
cur = cur.next;
l1 = l1 == null ? null : l1.next;
l2 = l2 == null ? null : l2.next;
}
return dummy.next;
}
}(code-box)
/**
* Definition for singly-linked list.
* 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) {
ListNode dummy;
int carry = 0;
ListNode* cur = &dummy;
while (l1 || l2 || carry) {
int s = (l1 ? l1->val : 0) + (l2 ? l2->val : 0) + carry;
carry = s / 10;
cur->next = new ListNode(s % 10);
cur = cur->next;
l1 = l1 ? l1->next : nullptr;
l2 = l2 ? l2->next : nullptr;
}
return dummy.next;
}
};(code-box)
/**
* Definition for singly-linked list.
* type ListNode struct {
* Val int
* Next *ListNode
* }
*/
func addTwoNumbers(l1 *ListNode, l2 *ListNode) *ListNode {
dummy := &ListNode{}
carry := 0
cur := dummy
for l1 != nil || l2 != nil || carry != 0 {
s := carry
if l1 != nil {
s += l1.Val
}
if l2 != nil {
s += l2.Val
}
carry = s / 10
cur.Next = &ListNode{s % 10, nil}
cur = cur.Next
if l1 != nil {
l1 = l1.Next
}
if l2 != nil {
l2 = l2.Next
}
}
return dummy.Next
}(code-box)
/**
* Definition for singly-linked list.
* 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 dummy = new ListNode();
let cur = dummy;
let sum = 0;
while (l1 != null || l2 != null || sum !== 0) {
if (l1 != null) {
sum += l1.val;
l1 = l1.next;
}
if (l2 != null) {
sum += l2.val;
l2 = l2.next;
}
cur.next = new ListNode(sum % 10);
cur = cur.next;
sum = Math.floor(sum / 10);
}
return dummy.next;
}(code-box)
// 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 {
pub fn add_two_numbers(
mut l1: Option<Box<ListNode>>,
mut l2: Option<Box<ListNode>>,
) -> Option<Box<ListNode>> {
let mut dummy = Some(Box::new(ListNode::new(0)));
let mut cur = &mut dummy;
let mut sum = 0;
while l1.is_some() || l2.is_some() || sum != 0 {
if let Some(node) = l1 {
sum += node.val;
l1 = node.next;
}
if let Some(node) = l2 {
sum += node.val;
l2 = node.next;
}
cur.as_mut().unwrap().next = Some(Box::new(ListNode::new(sum % 10)));
cur = &mut cur.as_mut().unwrap().next;
sum /= 10;
}
dummy.unwrap().next.take()
}
}(code-box)
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} l1
* @param {ListNode} l2
* @return {ListNode}
*/
var addTwoNumbers = function (l1, l2) {
const dummy = new ListNode();
let carry = 0;
let cur = dummy;
while (l1 || l2 || carry) {
const s = (l1?.val || 0) + (l2?.val || 0) + carry;
carry = Math.floor(s / 10);
cur.next = new ListNode(s % 10);
cur = cur.next;
l1 = l1?.next;
l2 = l2?.next;
}
return dummy.next;
};(code-box)
/**
* Definition for singly-linked list.
* public class ListNode {
* public int val;
* public ListNode next;
* public ListNode(int val=0, ListNode next=null) {
* this.val = val;
* this.next = next;
* }
* }
*/
public class Solution {
public ListNode AddTwoNumbers(ListNode l1, ListNode l2) {
ListNode dummy = new ListNode();
int carry = 0;
ListNode cur = dummy;
while (l1 != null || l2 != null || carry != 0) {
int s = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + carry;
carry = s / 10;
cur.next = new ListNode(s % 10);
cur = cur.next;
l1 = l1 == null ? null : l1.next;
l2 = l2 == null ? null : l2.next;
}
return dummy.next;
}
}(code-box)
/**
* Definition for a singly-linked list.
* class ListNode {
* public $val = 0;
* public $next = null;
* function __construct($val = 0, $next = null) {
* $this->val = $val;
* $this->next = $next;
* }
* }
*/
class Solution {
/**
* @param ListNode $l1
* @param ListNode $l2
* @return ListNode
*/
function addTwoNumbers($l1, $l2) {
$dummy = new ListNode(0);
$current = $dummy;
$carry = 0;
while ($l1 !== null || $l2 !== null) {
$x = $l1 !== null ? $l1->val : 0;
$y = $l2 !== null ? $l2->val : 0;
$sum = $x + $y + $carry;
$carry = (int) ($sum / 10);
$current->next = new ListNode($sum % 10);
$current = $current->next;
if ($l1 !== null) {
$l1 = $l1->next;
}
if ($l2 !== null) {
$l2 = $l2->next;
}
}
if ($carry > 0) {
$current->next = new ListNode($carry);
}
return $dummy->next;
}
}(code-box)
/**
* Definition for singly-linked list.
* public class ListNode {
* public var val: Int
* public var next: ListNode?
* public init() { self.val = 0; self.next = nil; }
* public init(_ val: Int) { self.val = val; self.next = nil; }
* public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
* }
*/
class Solution {
func addTwoNumbers(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
var dummy = ListNode.init()
var carry = 0
var l1 = l1
var l2 = l2
var cur = dummy
while l1 != nil || l2 != nil || carry != 0 {
let s = (l1?.val ?? 0) + (l2?.val ?? 0) + carry
carry = s / 10
cur.next = ListNode.init(s % 10)
cur = cur.next!
l1 = l1?.next
l2 = l2?.next
}
return dummy.next
}
}(code-box)
# Definition for singly-linked list.
# class ListNode
# attr_accessor :val, :next
# def initialize(val = 0, _next = nil)
# @val = val
# @next = _next
# end
# end
# @param {ListNode} l1
# @param {ListNode} l2
# @return {ListNode}
def add_two_numbers(l1, l2)
dummy = ListNode.new()
carry = 0
cur = dummy
while !l1.nil? || !l2.nil? || carry > 0
s = (l1.nil? ? 0 : l1.val) + (l2.nil? ? 0 : l2.val) + carry
carry = s / 10
cur.next = ListNode.new(s % 10)
cur = cur.next
l1 = l1.nil? ? l1 : l1.next
l2 = l2.nil? ? l2 : l2.next
end
dummy.next
end(code-box)
#[
# Driver code in the solution file
# Definition for singly-linked list.
type
Node[int] = ref object
value: int
next: Node[int]
SinglyLinkedList[T] = object
head, tail: Node[T]
]#
# More efficient code churning ...
proc addTwoNumbers(l1: var SinglyLinkedList, l2: var SinglyLinkedList): SinglyLinkedList[int] =
var
aggregate: SinglyLinkedList
psum: seq[char]
temp_la, temp_lb: seq[int]
while not l1.head.isNil:
temp_la.add(l1.head.value)
l1.head = l1.head.next
while not l2.head.isNil:
temp_lb.add(l2.head.value)
l2.head = l2.head.next
psum = reversed($(reversed(temp_la).join("").parseInt() + reversed(temp_lb).join("").parseInt()))
for i in psum: aggregate.append(($i).parseInt())
result = aggregate(code-box)
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* struct ListNode *next;
* };
*/
struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
struct ListNode* dummy = (struct ListNode*) malloc(sizeof(struct ListNode));
dummy->val = 0;
dummy->next = NULL;
struct ListNode* curr = dummy;
int carry = 0;
while (l1 != NULL || l2 != NULL || carry != 0) {
int sum = carry;
if (l1 != NULL) {
sum += l1->val;
l1 = l1->next;
}
if (l2 != NULL) {
sum += l2->val;
l2 = l2->next;
}
carry = sum / 10;
int val = sum % 10;
struct ListNode* newNode = (struct ListNode*) malloc(sizeof(struct ListNode));
newNode->val = val;
newNode->next = NULL;
curr->next = newNode;
curr = curr->next;
}
struct ListNode* result = dummy->next;
free(dummy);
return result;
}(code-box)
