feat(algorithms, graphs): reconstruct itinerary #144
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📝 WalkthroughWalkthroughAdds two graph algorithm features (Reconstruct Itinerary and Cat and Mouse) with implementations, READMEs, and tests; updates Changes
Sequence Diagram(s)(omitted — changes do not introduce multi-component sequential interactions meeting the diagram criteria) Estimated code review effort🎯 4 (Complex) | ⏱️ ~45 minutes Possibly related PRs
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Actionable comments posted: 2
🤖 Fix all issues with AI agents
In @algorithms/graphs/reconstruct_itinerary/__init__.py:
- Line 35: Update the inline comment "After this backtrack to the top airport in
the stack and continue to traaverse it's children" by fixing the typos: change
"traaverse" to "traverse" and "it's" to the possessive "its" so the comment
reads "After this backtrack to the top airport in the stack and continue to
traverse its children".
In @algorithms/graphs/reconstruct_itinerary/README.md:
- Line 34: The README uses the non-hyphenated phrase "Depth First Search";
update that occurrence to the standard hyphenated form "Depth-First Search"
(e.g., modify the line containing "Depth First Search" in the
algorithms/graphs/reconstruct_itinerary/README.md to read "Depth-First Search")
so terminology is consistent.
🧹 Nitpick comments (3)
algorithms/graphs/reconstruct_itinerary/__init__.py (2)
16-27: Consider usingdefaultdictfor graph construction.The manual dictionary initialization pattern could be simplified using
defaultdict(list), which is already imported (though used only in the second function).♻️ Optional refactor using defaultdict
- graph = {} + graph: DefaultDict[str, List[str]] = defaultdict(list) # Create a graph for each airport and keep list of airport reachable from it for src, dst in tickets: - if src in graph: - graph[src].append(dst) - else: - graph[src] = [dst] + graph[src].append(dst)
51-61: Consider adding a docstring for consistency.The first function has a docstring, but this function lacks one. Adding a docstring would maintain consistency and improve documentation.
📝 Add docstring
def find_itinerary_using_hierholzers(tickets: List[List[str]]) -> List[str]: + """ + Reconstructs the itinerary from a given list of tickets using Hierholzer's algorithm. + Args: + tickets (list): list of lists of tickets [departure, arrival] + Returns: + List[str]: reconstructed itinerary starting from JFK + """ flight_map: DefaultDict[str, List[str]] = defaultdict(list)algorithms/graphs/reconstruct_itinerary/test_reconstruct_itinerary.py (1)
9-205: Consider adding an edge case test for empty input.The test cases are comprehensive, covering various scenarios including simple paths, cycles, and complex branching. However, there's no test case for empty input (
[]), which is explicitly handled infind_itinerarybut not infind_itinerary_using_hierholzers.🧪 Add empty input test case
RECONSTRUCT_ITINERARY_TEST_CASES = [ + ([], []), # Empty input edge case ([["JFK", "EDU"], ["EDU", "LEX"], ["LEX", "MUO"]], ["JFK", "EDU", "LEX", "MUO"]),Note: This would also reveal that
find_itinerary_using_hierholzersreturns["JFK"]for empty input instead of[], which may need to be addressed in the implementation if consistent behavior is desired.
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DIRECTORY.mdalgorithms/graphs/reconstruct_itinerary/README.mdalgorithms/graphs/reconstruct_itinerary/__init__.pyalgorithms/graphs/reconstruct_itinerary/test_reconstruct_itinerary.py
🧰 Additional context used
🪛 LanguageTool
algorithms/graphs/reconstruct_itinerary/README.md
[grammar] ~34-~34: Use a hyphen to join words.
Context: ...ample_3.png) ## Related Topics - Depth First Search - Graph - Eulerian Circuit ...
(QB_NEW_EN_HYPHEN)
[style] ~78-~78: Using many exclamation marks might seem excessive (in this case: 15 exclamation marks for a text that’s 5949 characters long)
Context: ...s/reconstruct_itinerary_solution_1.png) 
🪛 markdownlint-cli2 (0.18.1)
algorithms/graphs/reconstruct_itinerary/README.md
48-48: Blank line inside blockquote
(MD028, no-blanks-blockquote)
DIRECTORY.md
111-111: Unordered list indentation
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327-327: Unordered list indentation
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🔇 Additional comments (11)
DIRECTORY.md (2)
111-112: LGTM!The new Reconstruct Itinerary entry follows the existing directory structure and indentation conventions. The static analysis hints about indentation are false positives since this file consistently uses 4-space indentation for nested list items throughout.
326-327: LGTM!The Reorder List entry is correctly placed and follows the established formatting conventions.
algorithms/graphs/reconstruct_itinerary/__init__.py (4)
1-2: LGTM!The imports are appropriate for the implementation. Using
DefaultDicttype hint withdefaultdictis a good practice for type clarity.
5-14: LGTM!The function signature with type hints and docstring is well-documented. The early return for empty input is appropriate.
37-48: LGTM!The stack-based traversal logic correctly implements the post-order pattern for Hierholzer's algorithm. The result reversal at the end produces the correct itinerary order.
Minor style note:
while stack:is slightly more Pythonic thanwhile len(stack) > 0:, but this is a negligible preference.
63-80: LGTM!The recursive DFS implementation correctly applies Hierholzer's algorithm. The post-order accumulation (appending after visiting all destinations) combined with the final reversal produces the correct itinerary. The nested function design is clean and maintains proper encapsulation.
algorithms/graphs/reconstruct_itinerary/README.md (3)
1-16: LGTM!The problem description is clear and well-documented with examples explaining lexicographical ordering. The constraints and notes are appropriately included.
38-58: LGTM!The solution explanation clearly describes Hierholzer's algorithm and the approach. The step-by-step breakdown of the algorithm is well-structured and educational.
Note: The static analysis hint about the blank line between blockquotes (line 48) can be safely ignored as the two blockquotes intentionally explain different concepts (Hierholzer's algorithm vs Eulerian path).
94-109: LGTM!The complexity analysis is thorough, explaining both the DFS traversal cost and the sorting overhead. The distinction between worst-case (star-shaped graph) and average scenarios is helpful.
algorithms/graphs/reconstruct_itinerary/test_reconstruct_itinerary.py (2)
1-7: LGTM!The imports are appropriate. Using
parameterizedfor test case expansion is a good practice that reduces code duplication.
208-223: LGTM!The test class structure is clean. Testing both implementations with the same expected outputs ensures behavioral consistency between the iterative and recursive approaches.
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Actionable comments posted: 2
🤖 Fix all issues with AI agents
In @algorithms/graphs/cat_and_mouse/__init__.py:
- Line 47: The condition uses identity comparison: replace the object identity
check "color[i2, j2, t2] is draw" with a value equality check using "==" so that
the code compares the value of color at indices i2, j2, t2 to draw; update the
conditional in the relevant function where color, i2, j2, t2, and draw are used
to use "==" instead of "is".
In @DIRECTORY.md:
- Around line 90-91: Fix markdown list indentation for the three sections
flagged by the linter: adjust the "Cat And Mouse" lines so the category header
"Cat And Mouse" is indented by 2 spaces and its entry "[Test Cat And
Mouse](...)" is indented by 4 spaces; do the same for "Reconstruct Itinerary"
(make the header 2 spaces and its test link 4 spaces) and "Reorder List" (header
2 spaces, entry 4 spaces) so they match the repository's consistent list
indentation pattern.
🧹 Nitpick comments (2)
algorithms/graphs/cat_and_mouse/__init__.py (2)
43-43: Consider renamingctowinnerfor clarity.The variable
cis used for both cat position (inparentsfunction) and the winning color here. Renaming towinneroroutcomewould improve readability.♻️ Suggested improvement
- i, j, t, c = queue.popleft() + i, j, t, winner = queue.popleft() # for every parent of this node i, j, t : for i2, j2, t2 in parents(i, j, t): # if this parent is not colored : if color[i2, j2, t2] == draw: # if the parent can make a winning move (ie. mouse to MOUSE), do so - if t2 == c: # winning move - color[i2, j2, t2] = c - queue.append((i2, j2, t2, c)) + if t2 == winner: # winning move + color[i2, j2, t2] = winner + queue.append((i2, j2, t2, winner))
5-10: Consider adding a docstring with doctests.Per the project's contribution guidelines, functions should include doctests. A docstring would document the expected behavior and provide inline tests.
📝 Example docstring
def cat_mouse_game(graph: List[List[int]]) -> int: """ Determine the winner of the Cat and Mouse game using retrograde analysis. Args: graph: Adjacency list where graph[a] lists all nodes connected to a. Mouse starts at node 1, cat at node 2, hole at node 0. Returns: 0 if the game is a draw, 1 if mouse wins, 2 if cat wins. >>> cat_mouse_game([[2,5],[3],[0,4,5],[1,4,5],[2,3],[0,2,3]]) 0 >>> cat_mouse_game([[1,3],[0],[3],[0,2]]) 1 """ n = len(graph) ...
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DIRECTORY.mdalgorithms/graphs/cat_and_mouse/README.mdalgorithms/graphs/cat_and_mouse/__init__.pyalgorithms/graphs/cat_and_mouse/test_cat_and_mouse.py
🧰 Additional context used
🧬 Code graph analysis (1)
algorithms/graphs/cat_and_mouse/test_cat_and_mouse.py (1)
algorithms/graphs/cat_and_mouse/__init__.py (1)
cat_mouse_game(5-60)
🪛 LanguageTool
algorithms/graphs/cat_and_mouse/README.md
[style] ~18-~18: Three successive sentences begin with the same word. Consider rewording the sentence or use a thesaurus to find a synonym.
Context: ...use reaches the Hole, the Mouse wins. - If ever a position is repeated (i.e., the ...
(ENGLISH_WORD_REPEAT_BEGINNING_RULE)
[style] ~79-~79: Consider using “who” when you are referring to a person instead of an object.
Context: ...mediate coloring"): If there is a child that is colored MOUSE, then this node will a...
(THAT_WHO)
[uncategorized] ~96-~96: Did you mean the adverb “anymore”?
Context: ...x works. Say we cannot color any nodes any more, and say from any node colored CAT or M...
(ANY_MORE)
🪛 markdownlint-cli2 (0.18.1)
DIRECTORY.md
90-90: Unordered list indentation
Expected: 2; Actual: 4
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91-91: Unordered list indentation
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329-329: Unordered list indentation
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algorithms/graphs/cat_and_mouse/README.md
45-45: Reference links and images should use a label that is defined
Missing link or image reference definition: "j"
(MD052, reference-links-images)
46-46: Reference links and images should use a label that is defined
Missing link or image reference definition: "j"
(MD052, reference-links-images)
🔇 Additional comments (3)
algorithms/graphs/cat_and_mouse/test_cat_and_mouse.py (1)
1-20: LGTM!The test file is well-structured with parameterized tests that align with the examples documented in the README. Test cases correctly validate the expected outcomes (0 for draw, 1 for mouse win).
algorithms/graphs/cat_and_mouse/README.md (1)
1-116: LGTM!The documentation comprehensively explains the Cat and Mouse game problem, constraints, and the minimax/percolation solution approach. The examples align with the test cases and implementation.
Note: The static analysis warnings about
[j]on lines 45-46 are false positives—these represent array indexing notation (graph[i][j]), not markdown reference links.algorithms/graphs/cat_and_mouse/__init__.py (1)
14-21: LGTM!The
parentsfunction correctly computes predecessor states:
- When it's cat's turn (
t == 2), find mouse moves that led here- When it's mouse's turn (
t == 1), find cat moves (excluding hole at node 0 viaif c2:)The
3 - ttoggle elegantly switches between turns 1 and 2.
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