Update Linked List Sequence - codepath/compsci_guides GitHub Wiki

Unit 5 Session 2 (Click for link to problem statements)

TIP102 Unit 5 Session 2 Standard (Click for link to problem statements)

Problem Highlights

  • 💡 Difficulty: Easy
  • ⏰ Time to complete: 10-15 mins
  • 🛠️ Topics: Linked Lists, Insertion

1: U-nderstand

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?
  • What happens if we want to insert nodes in the middle of the list?
    • You should update the next pointers of the appropriate nodes to insert the new nodes in the correct positions.
HAPPY CASE
Input: head = Node("Shy Guy") -> Node("Diddy Kong") -> Node("Dry Bones")
Output: Node("Shy Guy") -> Node("Link") -> Node("Diddy Kong") -> Node("Toad") -> Node("Dry Bones")
Explanation: The nodes "Link" and "Toad" are correctly inserted in the list.

EDGE CASE
Input: head = Node("Shy Guy")
Output: Node("Shy Guy")
Explanation: The list contains only one node, and no new nodes are added.

2: M-atch

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.

For Linked List problems, we want to consider the following approaches:

  • Insertion of nodes in a linked list
  • Updating pointers to maintain the correct sequence

3: P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Insert new nodes into the existing linked list by updating the next pointers of the relevant nodes.

1) Create the new nodes "Link" and "Toad".
2) Update the `next` pointer of the node "Shy Guy" to point to "Link", and update the `next` pointer of "Link" to point to "Diddy Kong".
3) Update the `next` pointer of the node "Diddy Kong" to point to "Toad", and update the `next` pointer of "Toad" to point to "Dry Bones".
4) Print the linked list to verify the order.

⚠️ Common Mistakes

  • Forgetting to update the next pointers correctly, leading to incorrect list sequences.
  • Not ensuring that the inserted nodes are properly connected to the rest of the list.

4: I-mplement

Implement the code to solve the algorithm.

class Node:
    def __init__(self, value, next=None):
        self.value = value
        self.next = next

# For testing
def print_linked_list(head):
    current = head
    while current:
        print(current.value, end=" -> " if current.next else "\n")
        current = current.next

shy_guy = Node("Shy Guy")
diddy_kong = Node("Diddy Kong")
dry_bones = Node("Dry Bones")
shy_guy.next = diddy_kong
diddy_kong.next = dry_bones

# Add code to update the list here
link = Node("Link")
toad = Node("Toad")

# Insert Link after Shy Guy
link.next = shy_guy.next
shy_guy.next = link

# Insert Toad after Diddy Kong
toad.next = diddy_kong.next
diddy_kong.next = toad

5: R-eview

Review the code by running specific example(s) and recording values (watchlist) of your code's variables along the way.

  • Check the order of the nodes after the insertions to ensure the linked list is correctly updated.

Example:

print("Current List:")
print_linked_list(shy_guy)
# Expected Output: "Shy Guy -> Link -> Diddy Kong -> Toad -> Dry Bones"

6: E-valuate

Evaluate the performance of your algorithm and state any strong/weak or future potential work.

  • Time Complexity: O(1) for each insertion since we are directly updating the pointers.
  • Space Complexity: O(1) because we are only adding a fixed number of new nodes.