# Add Two Numbers in Python

PythonServer Side ProgrammingProgramming

Suppose we have given two non-empty linked lists. These two lists are representing two non-negative integer numbers. The digits are stored in reverse order. Each of their nodes contains only one digit. Add the two numbers and return the result as a linked list. We are taking the assumption that the two numbers do not contain any leading zeros, except the number 0 itself. So if the numbers are 120 + 230, then the linked lists will be [0 → 2 → 1] + [0 → 3 → 2] = [0 → 5 → 3] = 350.

To solve this, we will follow these steps

• Take two lists l1 and l2. Initialize head and temp as null
• c := 0
• while l1 and l2 both are non-empty lists
• if l1 is non-empty, then set a := 0, otherwise set a := l1.val
• if l2 is non-empty, then set b := 0, otherwise set b := l2.val
• n := a + b + c
• if n > 9, then c := 1 otherwise 0
• node := create a new node with value n mod 10
• head := node and temp := node

• otherwise
• l1 := next node of l1, if l1 exists
• l2 := next node of l2, if l2 exists
• if c is non-zero, then
• node := new node with value 1, next of head := node
• return temp

## Example(Python)

Let us see the following implementation to get a better understanding

Live Demo

class ListNode:
def __init__(self, data, next = None):
self.val = data
self.next = next
def make_list(elements):
for element in elements[1:]:
while ptr.next:
ptr = ptr.next
ptr.next = ListNode(element)
print('[', end = "")
while ptr:
print(ptr.val, end = ", ")
ptr = ptr.next
print(']')
class Solution:
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
temp = None
c = 0
while l1 or l2:
if not l1:
a= 0
else:
a = l1.val
if not l2:
b=0
else:
b = l2.val
n = a +b + c
c = 1 if n>9 else 0
node = ListNode(n%10)
temp = node
else:
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
if c:
node = ListNode(1)
return temp
ob1 = Solution()
l1 = make_list([0,2,1])
l2 = make_list([0,3,2])
print_list(ob1.addTwoNumbers(l1, l2))

## Input

[0,2,1]
[0,3,2]

## Output

[0,5,3]
Published on 30-Jan-2020 06:58:50