Originally from Unit 6 Session 2 (Click for link to problem statements)
Reviewed in Unit 10 Session 2
TIP102 Unit 5 Session 2 Advanced (Click for link to problem statements)
Understand what the interviewer is asking for by using test cases and questions about the problem.
- Established a set (2-3) of test cases to verify their own solution later.
- Established a set (1-2) of edge cases to verify their solution handles complexities.
- Have fully understood the problem and have no clarifying questions.
- Have you verified any Time/Space Constraints for this problem?
HAPPY CASE
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807, so the list is 7 -> 0 -> 8.
EDGE CASE
Input: (0) + (0)
Output: 0
Explanation: 0 + 0 = 0, no carry is involved and only one node is needed.
Match what this problem looks like to known categories of problems, e.g. Linked List or Dynamic Programming, and strategies or patterns in those categories.
This is a problem involving arithmetic operations directly on linked lists, typically solved using a carry variable and direct digit-wise addition.
Plan the solution with appropriate visualizations and pseudocode.
General Idea: Simultaneously traverse both linked lists, adding corresponding digits along with any carry, and form a new linked list with the sum.
1) Initialize a temp node to handle the result and a pointer for the current node in the result list.
2) Traverse both lists, adding values of corresponding nodes plus any carry.
3) Store the units digit in the current node of the result list and update the carry.
4) Continue until both lists are exhausted and any carry is added.
5) Ensure to handle any remaining nodes from the longer list.
⚠️ Common Mistakes
Implement the code to solve the algorithm.
def add_two_numbers(head_a, head_b):
# Temp head to simplify handling the result list
temp_head = Node()
current = temp_head
carry = 0
a_current = head_a
b_current = head_b
while a_current or b_current or carry:
val_a = a_current.value if a_current else 0
val_b = b_current.value if b_current else 0
# Calculate the sum of values and the carry
sum_val = val_a + val_b + carry
carry = sum_val // 10
sum_val = sum_val % 10
# Append the result to the new list
current.next = Node(sum_val)
current = current.next
# Move to the next elements in the lists
if a_current:
a_current = a_current.next
if b_current:
b_current = b_current.next
return temp_head.next
Review the code by running specific example(s) and recording values (watchlist) of your code's variables along the way.
Evaluate the performance of your algorithm and state any strong/weak or future potential work.
O(max(m, n))
where m
and n
are the lengths of the two lists, since each node in both lists needs to be processed.O(max(m, n))
for the new list that might be as long as the longer of the two input lists plus one more node for a possible carry.