Linked List Basics 10 XP Easy

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A Linked List is a data structure where each element (node) contains data AND a pointer to the next node. Unlike arrays, elements aren't stored next to each other in memory! 🔗

💡 Think of it like this: Imagine a treasure hunt. Each clue has a piece of paper with a message AND directions to the next clue. You follow the chain: Clue 1 → Clue 2 → Clue 3 → End. That's a linked list!

💭 Go for it! Apply the approach above in your own code. If you get stuck, use the hint below! 🔥

Array vs Linked List:

✅ Insert/Delete at beginning: Linked List O(1) vs Array O(n)
❌ Access by index: Array O(1) vs Linked List O(n)
✅ Dynamic size: Linked Lists grow/shrink easily, no resizing needed
❌ Memory: Linked Lists use extra memory for pointers

Common linked list techniques you'll use in interviews:

🐢🐇 Fast & Slow pointers: Detect cycles, find middle
↩️ Reverse: Flip all the arrows (3 pointer technique)
🔀 Merge: Combine two sorted lists
👻 Dummy node: Simplify edge cases (empty list, single element)

📋 Instructions

Create a linked list with values 1 → 2 → 3 → 4 → 5. Then traverse it and print each value on a separate line.

Create head = ListNode(1), then chain .next nodes. Traverse with a while loop: while current is not None, print val, move to current.next.

⚠️ Try solving it yourself first — you'll learn more!

# A Node has data + a pointer to next
class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

# Building: 1 → 2 → 3 → None
head = ListNode(1)
head.next = ListNode(2)
head.next.next = ListNode(3)

# Traversal:
current = head
while current:
    print(current.val, end=' → ')
    current = current.next
# Output: 1 → 2 → 3 →

🧪 Test Cases

Input

Run your code

Expected

1
2
3
...

Expected output (5 lines)

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main.py

Hi! I'm Rex 👋

Output

Ready. Press ▶ Run or Ctrl+Enter.

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