MEDIUM NC#38 Blind #44 Linked List

19. Remove Nth Node From End of List

📖 Problem

Given the head of a linked list, remove the nth node from the end of the list and return its head.

🧠 Visual Learning Aid

1 Model the input into the right structure
2 Choose the core technique and invariant
3 Execute step-by-step with a sample
4 Validate complexity and edge cases

JS/TS Refreshers

  • •Array methods (`push`, `pop`, `shift`, `slice`)
  • •Object/Map/Set usage patterns
  • •Function parameter and return typing
  • •In-place array updates
  • •Sorted array traversal
  • •Boundary condition checks

Logical Thinking Concepts

  • •Define invariants before coding
  • •Check edge cases first (`[]`, single element, duplicates)
  • •Estimate time/space before implementation
  • •Apply Two Pointers reasoning pattern

💡 Approach

  • → Use two pointers with gap of n
  • → Move fast pointer n+1 steps ahead
  • → When fast reaches end, slow is at the node before target
  • → Use dummy node to handle edge case of removing head
  • → Time: O(n), Space: O(1)

🧭 Prerequisites

#2 Add Two Numbers #206 Reverse Linked List

🛠️ Hints & Pitfalls

Hints

  • •Use two pointers with gap of n
  • •Move fast pointer n+1 steps ahead
  • •When fast reaches end, slow is at the node before target

Common Pitfalls

  • •Use dummy node to handle edge case of removing head
  • •Time: O(n), Space: O(1)

🧪 Test Cases

Hidden tests on submit: 1

Test Case 1
Not run
Input:
removeNthFromEnd(arrayToList([1,2,3,4,5]), 2);
Expected:
{"val":1,"next":{"val":2,"next":{"val":3,"next":{"val":5,"next":null}}}}
Test Case 2
Not run
Input:
removeNthFromEnd(arrayToList([1]), 1);
Expected:
null
Test Case 3
Not run
Input:
removeNthFromEnd(arrayToList([1,2]), 1);
Expected:
{"val":1,"next":null}

📝 Code Editor

📚 Reference Solution

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🔗 Related Problems

#2 Add Two Numbers #21 Merge Two Sorted Lists #23 Merge k Sorted Lists #25 Reverse Nodes in k-Group #138 Copy List with Random Pointer
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