The Runtime Theory
mediumLeetCode#matrix#transpose#reverse

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Rotate an n-by-n matrix 90 degrees clockwise in place.

The Runtime Theory Team25 min read
Solve it

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

Sample cases

inmatrix=[[1,2,3],[4,5,6],[7,8,9]]

out[[7,4,1],[8,5,2],[9,6,3]]

inmatrix=[[1]]

out[[1]]

inmatrix=[[1,2],[3,4]]

out[[3,1],[4,2]]

Rotate an n-by-n matrix 90 degrees clockwise in place.

A good solution should

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

Reasoning prompt

Compare layer-by-layer four-way swaps with transpose then row reversal. Show why the result uses no matrix-sized buffer.

Use the linked judge for the canonical challenge. The examples above are compact TRT checks; create additional tests around the boundary most likely to break your invariant.

More practice in this topic

easy · arraysContains Duplicatemedium · arraysEncode and Decode a List of Stringsmedium · arraysGroup Anagrams

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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