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# Program to find numbers represented as linked lists in Python

Suppose we have two singly linked list L1 and L2, each representing a number with least significant digits first, we have to find the summed linked list.

So, if the input is like L1 = [5,6,4] L2 = [2,4,8], then the output will be [7, 0, 3, 1, ]

To solve this, we will follow these steps:

carry := 0

res := a new node with value 0

curr := res

while L1 is not empty or L2 is not empty or carry is non-zero, do

l0_val := value of L1 if L1 is not empty otherwise 0

l1_val := value of L2 if L2 is not empty otherwise 0

sum_ := l0_val + l1_val

carry := quotient of (sum_ + carry) / 10

add_val := remainder of (sum_ + carry) / 10

curr.next := a new node with value add_val

curr := next of curr

L1 := next of L1 if L1 is not empty otherwise null

L2 := next of L2 if L2 is not empty otherwise null

next of curr := null

return next of res

Let us see the following implementation to get better understanding:

## Example

class ListNode: def __init__(self, data, next = None): self.val = data self.next = next def make_list(elements): head = ListNode(elements[0]) for element in elements[1:]: ptr = head while ptr.next: ptr = ptr.next ptr.next = ListNode(element) return head def print_list(head): ptr = head print('[', end = "") while ptr: print(ptr.val, end = ", ") ptr = ptr.next print(']') class Solution: def solve(self, L1, L2): carry = 0 res = ListNode(0) curr = res while L1 or L2 or carry: l0_val = L1.val if L1 else 0 l1_val = L2.val if L2 else 0 sum_ = l0_val + l1_val carry, add_val = divmod(sum_ + carry, 10) curr.next = ListNode(add_val) curr = curr.next L1 = L1.next if L1 else None L2 = L2.next if L2 else None curr.next = None return res.next ob = Solution() L1 = make_list([5,6,4]) L2 = make_list([2,4,8]) print_list(ob.solve(L1, L2))

## Input

[5,6,4], [2,4,8]

## Output

[7, 0, 3, 1, ]

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