The Runtime Theory
mediumLeetCode#two-pointers#sentinel

Remove Nth Node From End of List

Remove the nth node from the end using one pass when possible.

The Runtime Theory Team25 min read
Solve it

Solving happens on the judge — come back and mark it done

Sample cases

inhead=[1,2,3,4,5], n=2

out[1,2,3,5]

inhead=[1], n=1

out[]

inhead=[1,2], n=2

out[2]

Remove the nth node from the end using one pass when possible.

A good solution should

  • State the invariant or decision rule that makes the approach correct.
  • Explain the time and space complexity in terms of the input sizes and required output.
  • Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.

Reasoning prompt

A sentinel simplifies removal of the head. Maintain a fixed pointer gap and state what happens when the gap reaches the end.

Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.

More practice in this topic

medium · linked listsAdd Two Numbersmedium · linked listsCopy List with Random Pointermedium · linked listsFind the Duplicate Number

One dispatch a week

The trace behind each problem, the tradeoff that explains it, and one technical dispatch per week — no noise.

One technical dispatch per week. No noise.

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