The example they give you basically hands you the answer if you stare at it long enough.
Clarify the problem constraints and confirm in-place rotation with O(1) extra space. Explain the two-step approach: first transpose the matrix (swap elements across the main diagonal), then reverse each row. This achieves the 90-degree clockwise rotation with constant extra space.
Pro tip: Mention that the rotation can also be done by reversing rows first then transposing, or by rotating in cycles of four elements; showing multiple valid approaches demonstrates depth. Also, discuss edge cases like 1x1 matrix and empty input.
Confirm that the matrix is N×N, rotation is 90 degrees clockwise, and it must be done in-place with O(1) extra space. Ask about input constraints and expected output.
Select the transpose-then-reverse method: transpose the matrix by swapping matrix[i][j] with matrix[j][i] for i < j, then reverse each row.
Iterate over the upper triangle (i from 0 to n-1, j from i+1 to n-1) and swap elements to transpose the matrix.
For each row, swap elements from the ends moving inward to reverse the row, completing the clockwise rotation.
State that time complexity is O(N^2) as each element is visited constant times, and space complexity is O(1) since only a few variables are used.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.