Leetcode 19 Remove Nth Node From End of List Java Solution
// SOLVING THIS WITH AN AI ASSISTANT (2026)
If you are working through this problem with an AI coding assistant — Claude, ChatGPT, Cursor chat, Gemini, GitHub Copilot, Aider, or any agent — the goal isn’t to ask for the answer. It is to use the tool to understand the pattern. The prompt sequence I’d run:
- Spec it back to me first. “In your own words, what is this problem actually testing? What’s the smallest example that fails the naive approach?”
- Brute-force first, optimize after. “Write the simplest correct solution, even if it’s O(n²). Don’t optimize. Just make it correct, with comments explaining each step.”
- Ask for the upgrade. “Now show me the optimal solution. What insight makes it possible? What pattern is this an instance of?”
- Stress-test it. “Generate 10 edge cases — empty input, single element, duplicates, max size, sorted, reverse-sorted. Run my solution against each.”
The pattern matters more than the answer. If the agent just hands you optimized code, you’ve trained yourself to lose interviews.
Given a linked list, remove the n-th node from the end of list and return its head.
Example:
Given linked list: 1->2->3->4->5, and n = 2. After removing the second node from the end, the linked list becomes 1->2->3->5. Solution 1:
public class Solution {
public ListNode removeNthFromEnd(ListNode head, int n) {
if(head == null) return null;
int count = 0;
ListNode temp = head;
ListNode returnNode = head;
ListNode before = null;
while(temp!=null){
temp = temp.next;
count++;
}
for(int i = 0;head!=null && i<count-n;i++){
before = head;
head = head.next;
}
if(returnNode == head){
head = head.next;
returnNode = head;
}else{
before.next = head.next;
}
return returnNode;
}
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