Algorithm Notes
Summary: Add Two Numbers — notes not yet curated.
Time: Estimate via loops/recurrences; common classes: O(1), O(log n), O(n), O(n log n), O(n^2)
Space: Count auxiliary structures and recursion depth.
Tip: See the Big-O Guide for how to derive bounds and compare trade-offs.
Big-O Guide
Source
"""
Add Two Numbers
Problem: Add Two Numbers
LeetCode link: https://leetcode.com/problems/add-two-numbers/
Description: Add two numbers represented as linked lists and return head of result list.
"""
from src.interview_workbook.leetcode._nodes import ListNode
from src.interview_workbook.leetcode._registry import register_problem
from src.interview_workbook.leetcode._types import Category, Difficulty
class Solution:
def solve(self, *args):
"""
Add two numbers represented by linked lists.
Args: l1, l2 (ListNode)
Returns: ListNode (head of result list)
"""
l1, l2 = args
dummy = ListNode(0)
curr = dummy
carry = 0
while l1 or l2 or carry:
val1 = l1.val if l1 else 0
val2 = l2.val if l2 else 0
s = val1 + val2 + carry
carry = s // 10
curr.next = ListNode(s % 10)
curr = curr.next
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
return dummy.next
def demo():
"""Run a simple demonstration for Add Two Numbers problem."""
from src.interview_workbook.leetcode._nodes import ListNode
def build_list(nums):
dummy = ListNode(0)
curr = dummy
for n in nums:
curr.next = ListNode(n)
curr = curr.next
return dummy.next
def list_to_str(node):
vals = []
while node:
vals.append(str(node.val))
node = node.next
return "->".join(vals)
s = Solution()
l1 = build_list([2, 4, 3]) # represents 342
l2 = build_list([5, 6, 4]) # represents 465
result = s.solve(l1, l2) # should represent 807 -> [7,0,8]
return f"243 + 564 -> {list_to_str(result)}"
register_problem(
id=2,
slug="add_two_numbers",
title="Add Two Numbers",
category=Category.LINKED_LIST,
difficulty=Difficulty.MEDIUM,
tags=["linked_list", "math"],
url="https://leetcode.com/problems/add-two-numbers/",
notes="",
)