feat(algorithms matrix): transpose a matrix#184
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BrianLusina merged 2 commits intomainfrom Mar 2, 2026
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📝 WalkthroughWalkthroughThe PR reorganises the transpose function from Changes
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~25 minutes Possibly related PRs
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Actionable comments posted: 5
🧹 Nitpick comments (1)
algorithms/matrix/transpose/test_transpose_matrix.py (1)
6-36: Add an empty-matrix test case for branch coverage.The implementation handles
[]explicitly, but this path is not covered by current parametrised cases.💡 Proposed test addition
TRANSPOSE_MATRIX_TEST_CASES = [ + ( + [], + [], + ), ( [ [1, 2], ],🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed. In `@algorithms/matrix/transpose/test_transpose_matrix.py` around lines 6 - 36, Add a test case for the empty matrix into TRANSPOSE_MATRIX_TEST_CASES so the branch that handles [] is exercised; specifically append a tuple ([], []) to TRANSPOSE_MATRIX_TEST_CASES (the input should be an empty list and the expected output should also be an empty list) so the parametrised test (e.g., test_transpose_matrix) will cover the explicit [] handling in the transpose implementation.
🤖 Prompt for all review comments with AI agents
Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@algorithms/matrix/transpose/__init__.py`:
- Around line 28-36: The function transpose_matrix currently assumes rectangular
input and uses n_cols = len(matrix[0]) then indexes each row, which can raise
IndexError for jagged lists; before creating transposed_matrix, compute n_rows =
len(matrix) and n_cols = len(matrix[0]) and then validate every row in matrix
has length == n_cols (e.g., loop over rows and compare len(row)), and if any
differ raise a ValueError with a clear message (e.g., "transpose_matrix expects
a rectangular matrix; row X has length Y != n_cols"). Ensure this validation
occurs before allocating transposed_matrix and before the nested loop that
assigns transposed_matrix[col][row] = value.
- Around line 11-14: The final .strip() call in the transpose implementation
removes meaningful leading/trailing spaces (breaking outputs that start with
spaces or consist only of spaces); update the return of the function (the
expression that currently does "return \"\\n\".join(...).strip()") to not use
.strip() — either remove it entirely or replace it with .rstrip("\n") if you
only want to drop a trailing newline, so that leading spaces and all-space rows
are preserved by the transpose function.
In `@algorithms/matrix/transpose/README.md`:
- Around line 136-137: Fix the minor wording typo in the hints section by
changing the phrase "should be become" to "should become" in the sentence that
currently reads "Each column in the matrix should be become a row in the
transpose of the matrix." in the README.md transpose hints; ensure the corrected
sentence reads "Each column in the matrix should become a row in the transpose
of the matrix." to maintain clarity.
- Around line 24-27: The README for the matrix transpose exercise documents
padding direction incorrectly: the bullet that reads "Pad to the left with
spaces." should be changed to "Pad to the right with spaces." to match the
examples and implementation; update that sentence in the transpose README so it
explicitly states right-padding (and leave the "Don't pad to the right." line
removed or corrected accordingly).
- Around line 9-53: The fenced code blocks in README.md examples (the blocks
containing "ABC\nDEF", "AD\nBE\nCF", "ABC\nDE", "AD\nBE\nC", "AB\nDEF", and the
final "AD\nBE\n F" example) need explicit language identifiers to satisfy
markdown linting; update each opening triple-backtick so it reads ```text
instead of ``` for those specific examples so MD040 warnings are resolved.
---
Nitpick comments:
In `@algorithms/matrix/transpose/test_transpose_matrix.py`:
- Around line 6-36: Add a test case for the empty matrix into
TRANSPOSE_MATRIX_TEST_CASES so the branch that handles [] is exercised;
specifically append a tuple ([], []) to TRANSPOSE_MATRIX_TEST_CASES (the input
should be an empty list and the expected output should also be an empty list) so
the parametrised test (e.g., test_transpose_matrix) will cover the explicit []
handling in the transpose implementation.
ℹ️ Review info
Configuration used: Organization UI
Review profile: CHILL
Plan: Pro
📒 Files selected for processing (9)
DIRECTORY.mdalgorithms/matrix/transpose/README.mdalgorithms/matrix/transpose/__init__.pyalgorithms/matrix/transpose/test_transpose.pyalgorithms/matrix/transpose/test_transpose_matrix.pyalgorithms/transpose/README.mdalgorithms/transpose/__init__.pybit_manipulation/sum_two_integers/__init__.pybit_manipulation/sum_two_integers/test_sum_of_two_integers.py
💤 Files with no reviewable changes (2)
- algorithms/transpose/README.md
- algorithms/transpose/init.py
Comment on lines
+11
to
+14
| lines = input_lines.split("\n") | ||
| zipped = map(list, [line.ljust(len(max(lines, key=len))) for line in lines]) | ||
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| return "\n".join("".join(line) for line in zip(*zipped)).strip() |
Contributor
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transpose removes meaningful whitespace with global strip().
At Line 14, .strip() can delete valid characters (e.g. leading spaces in the first output row, or all-space outputs), which breaks the transpose contract.
💡 Proposed fix
def transpose(input_lines: str) -> str:
@@
- lines = input_lines.split("\n")
- zipped = map(list, [line.ljust(len(max(lines, key=len))) for line in lines])
-
- return "\n".join("".join(line) for line in zip(*zipped)).strip()
+ lines = input_lines.split("\n")
+ max_cols = max(len(line) for line in lines) if lines else 0
+ output_lines: List[str] = []
+
+ for col in range(max_cols):
+ row_chars: List[str] = []
+ for row_idx, line in enumerate(lines):
+ if col < len(line):
+ row_chars.append(line[col])
+ elif any(col < len(next_line) for next_line in lines[row_idx + 1 :]):
+ row_chars.append(" ")
+ output_lines.append("".join(row_chars))
+
+ return "\n".join(output_lines)🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@algorithms/matrix/transpose/__init__.py` around lines 11 - 14, The final
.strip() call in the transpose implementation removes meaningful
leading/trailing spaces (breaking outputs that start with spaces or consist only
of spaces); update the return of the function (the expression that currently
does "return \"\\n\".join(...).strip()") to not use .strip() — either remove it
entirely or replace it with .rstrip("\n") if you only want to drop a trailing
newline, so that leading spaces and all-space rows are preserved by the
transpose function.
Comment on lines
+28
to
+36
| n_rows = len(matrix) | ||
| n_cols = len(matrix[0]) | ||
|
|
||
| transposed_matrix = [[0] * n_rows for _ in range(n_cols)] | ||
|
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| for row in range(n_rows): | ||
| for col in range(n_cols): | ||
| value = matrix[row][col] | ||
| transposed_matrix[col][row] = value |
Contributor
There was a problem hiding this comment.
Validate rectangular input in transpose_matrix.
At Line 35, jagged input can trigger IndexError. It is safer to fail fast with a clear ValueError.
💡 Proposed fix
n_rows = len(matrix)
n_cols = len(matrix[0])
+ if any(len(row) != n_cols for row in matrix):
+ raise ValueError("All rows in `matrix` must have the same length")🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@algorithms/matrix/transpose/__init__.py` around lines 28 - 36, The function
transpose_matrix currently assumes rectangular input and uses n_cols =
len(matrix[0]) then indexes each row, which can raise IndexError for jagged
lists; before creating transposed_matrix, compute n_rows = len(matrix) and
n_cols = len(matrix[0]) and then validate every row in matrix has length ==
n_cols (e.g., loop over rows and compare len(row)), and if any differ raise a
ValueError with a clear message (e.g., "transpose_matrix expects a rectangular
matrix; row X has length Y != n_cols"). Ensure this validation occurs before
allocating transposed_matrix and before the nested loop that assigns
transposed_matrix[col][row] = value.
Comment on lines
+9
to
+53
| ``` | ||
| ABC | ||
| DEF | ||
| ``` | ||
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| is given by: | ||
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| ``` | ||
| AD | ||
| BE | ||
| CF | ||
| ``` | ||
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| Rows become columns and columns become rows. See <https://en.wikipedia.org/wiki/Transpose>. | ||
|
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| If the input has rows of different lengths, this is to be solved as follows: | ||
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| - Pad to the left with spaces. | ||
| - Don't pad to the right. | ||
|
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| Therefore, transposing this matrix: | ||
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| ``` | ||
| ABC | ||
| DE | ||
| ``` | ||
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| results in: | ||
|
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| ``` | ||
| AD | ||
| BE | ||
| C | ||
| ``` | ||
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| And transposing: | ||
|
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| ``` | ||
| AB | ||
| DEF | ||
| ``` | ||
|
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| results in: | ||
|
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| ``` |
Contributor
There was a problem hiding this comment.
Specify code fence languages to satisfy markdown linting.
The fenced blocks in this range should include a language identifier (e.g. text) to resolve MD040 warnings.
💡 Proposed fix
-```
+```text
ABC
DEF@@
- +text
AD
BE
CF
@@
-```
+```text
ABC
DE
@@
- +text
AD
BE
C
@@
-```
+```text
AB
DEF
@@
- +text
AD
BE
F
🧰 Tools
🪛 markdownlint-cli2 (0.21.0)
[warning] 9-9: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
[warning] 16-16: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
[warning] 31-31: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
[warning] 38-38: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
[warning] 46-46: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
[warning] 53-53: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@algorithms/matrix/transpose/README.md` around lines 9 - 53, The fenced code
blocks in README.md examples (the blocks containing "ABC\nDEF", "AD\nBE\nCF",
"ABC\nDE", "AD\nBE\nC", "AB\nDEF", and the final "AD\nBE\n F" example) need
explicit language identifiers to satisfy markdown linting; update each opening
triple-backtick so it reads ```text instead of ``` for those specific examples
so MD040 warnings are resolved.
Comment on lines
+24
to
+27
| If the input has rows of different lengths, this is to be solved as follows: | ||
|
|
||
| - Pad to the left with spaces. | ||
| - Don't pad to the right. |
Contributor
There was a problem hiding this comment.
Padding direction is documented incorrectly.
At Line 26, the rule should be right-padding, not left-padding, to match the examples and implementation behaviour.
💡 Proposed fix
-- Pad to the left with spaces.
+- Pad to the right with spaces.📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
Suggested change
| If the input has rows of different lengths, this is to be solved as follows: | |
| - Pad to the left with spaces. | |
| - Don't pad to the right. | |
| If the input has rows of different lengths, this is to be solved as follows: | |
| - Pad to the right with spaces. | |
| - Don't pad to the right. |
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@algorithms/matrix/transpose/README.md` around lines 24 - 27, The README for
the matrix transpose exercise documents padding direction incorrectly: the
bullet that reads "Pad to the left with spaces." should be changed to "Pad to
the right with spaces." to match the examples and implementation; update that
sentence in the transpose README so it explicitly states right-padding (and
leave the "Don't pad to the right." line removed or corrected accordingly).
Comment on lines
+136
to
+137
| - Each column in the matrix should be become a row in the transpose of the matrix. Each row in the matrix should become | ||
| a column in the transpose of the matrix. |
Contributor
There was a problem hiding this comment.
Minor wording typo in hints section.
At Line 136, “should be become” should be “should become”.
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.
In `@algorithms/matrix/transpose/README.md` around lines 136 - 137, Fix the minor
wording typo in the hints section by changing the phrase "should be become" to
"should become" in the sentence that currently reads "Each column in the matrix
should be become a row in the transpose of the matrix." in the README.md
transpose hints; ensure the corrected sentence reads "Each column in the matrix
should become a row in the transpose of the matrix." to maintain clarity.
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Describe your change:
Transpose a matrix
Checklist:
Fixes: #{$ISSUE_NO}.Summary by CodeRabbit
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