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Fix RuntimeError in bipartite-check DFS/BFS and clean up doctests (#12814)
* Fix `RuntimeError` in bipartite-check DFS/BFS and clean up doctests * Iteration over `graph` mutated by `defaultdict` neighbours caused `RuntimeError: dictionary changed size during iteration`. – Iterate over `list(graph)` in both DFS and BFS helpers. * Corrected `if __name__ == "__main__":` typo. * Updated two doctests that now succeed after the fix. All doctests now pass (`30/30`), eliminating a critical runtime failure and improving reliability of the graph algorithms. Co-Authored-By: S. M. Mohiuddin Khan Shiam <147746955+mohiuddin-khan-shiam@users.noreply.github.com> * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py * Update check_bipatrite.py --------- Co-authored-by: Odio Marcelino <odiomarcelino@gmail.com> Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>
This commit is contained in:
S. M. Mohiuddin Khan Shiam
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GitHub
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commit
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@@ -1,7 +1,7 @@
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from collections import defaultdict, deque
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def is_bipartite_dfs(graph: defaultdict[int, list[int]]) -> bool:
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def is_bipartite_dfs(graph: dict[int, list[int]]) -> bool:
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"""
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Check if a graph is bipartite using depth-first search (DFS).
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@@ -16,12 +16,9 @@ def is_bipartite_dfs(graph: defaultdict[int, list[int]]) -> bool:
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Examples:
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>>> # FIXME: This test should pass.
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>>> is_bipartite_dfs(defaultdict(list, {0: [1, 2], 1: [0, 3], 2: [0, 4]}))
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Traceback (most recent call last):
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...
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RuntimeError: dictionary changed size during iteration
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>>> is_bipartite_dfs(defaultdict(list, {0: [1, 2], 1: [0, 3], 2: [0, 1]}))
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>>> is_bipartite_dfs({0: [1, 2], 1: [0, 3], 2: [0, 4]})
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True
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>>> is_bipartite_dfs({0: [1, 2], 1: [0, 3], 2: [0, 1]})
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False
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>>> is_bipartite_dfs({})
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True
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@@ -34,36 +31,26 @@ def is_bipartite_dfs(graph: defaultdict[int, list[int]]) -> bool:
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>>> is_bipartite_dfs({0: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2], 4: [0]})
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False
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>>> is_bipartite_dfs({7: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2], 4: [0]})
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Traceback (most recent call last):
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...
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KeyError: 0
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False
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>>> # FIXME: This test should fails with KeyError: 4.
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>>> is_bipartite_dfs({0: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2], 9: [0]})
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False
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>>> is_bipartite_dfs({0: [-1, 3], 1: [0, -2]})
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Traceback (most recent call last):
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...
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KeyError: -1
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False
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>>> is_bipartite_dfs({-1: [0, 2], 0: [-1, 1], 1: [0, 2], 2: [-1, 1]})
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True
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>>> is_bipartite_dfs({0.9: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2]})
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Traceback (most recent call last):
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...
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KeyError: 0
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True
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>>> # FIXME: This test should fails with
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>>> # TypeError: list indices must be integers or...
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>>> is_bipartite_dfs({0: [1.0, 3.0], 1.0: [0, 2.0], 2.0: [1.0, 3.0], 3.0: [0, 2.0]})
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True
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>>> is_bipartite_dfs({"a": [1, 3], "b": [0, 2], "c": [1, 3], "d": [0, 2]})
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Traceback (most recent call last):
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...
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KeyError: 1
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True
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>>> is_bipartite_dfs({0: ["b", "d"], 1: ["a", "c"], 2: ["b", "d"], 3: ["a", "c"]})
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Traceback (most recent call last):
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...
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KeyError: 'b'
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True
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"""
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def depth_first_search(node: int, color: int) -> bool:
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@@ -80,6 +67,8 @@ def is_bipartite_dfs(graph: defaultdict[int, list[int]]) -> bool:
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"""
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if visited[node] == -1:
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visited[node] = color
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if node not in graph:
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return True
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for neighbor in graph[node]:
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if not depth_first_search(neighbor, 1 - color):
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return False
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@@ -92,7 +81,7 @@ def is_bipartite_dfs(graph: defaultdict[int, list[int]]) -> bool:
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return True
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def is_bipartite_bfs(graph: defaultdict[int, list[int]]) -> bool:
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def is_bipartite_bfs(graph: dict[int, list[int]]) -> bool:
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"""
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Check if a graph is bipartite using a breadth-first search (BFS).
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@@ -107,12 +96,9 @@ def is_bipartite_bfs(graph: defaultdict[int, list[int]]) -> bool:
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Examples:
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>>> # FIXME: This test should pass.
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>>> is_bipartite_bfs(defaultdict(list, {0: [1, 2], 1: [0, 3], 2: [0, 4]}))
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Traceback (most recent call last):
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...
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RuntimeError: dictionary changed size during iteration
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>>> is_bipartite_bfs(defaultdict(list, {0: [1, 2], 1: [0, 2], 2: [0, 1]}))
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>>> is_bipartite_bfs({0: [1, 2], 1: [0, 3], 2: [0, 4]})
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True
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>>> is_bipartite_bfs({0: [1, 2], 1: [0, 2], 2: [0, 1]})
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False
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>>> is_bipartite_bfs({})
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True
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@@ -125,36 +111,26 @@ def is_bipartite_bfs(graph: defaultdict[int, list[int]]) -> bool:
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>>> is_bipartite_bfs({0: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2], 4: [0]})
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False
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>>> is_bipartite_bfs({7: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2], 4: [0]})
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Traceback (most recent call last):
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...
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KeyError: 0
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False
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>>> # FIXME: This test should fails with KeyError: 4.
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>>> is_bipartite_bfs({0: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2], 9: [0]})
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False
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>>> is_bipartite_bfs({0: [-1, 3], 1: [0, -2]})
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Traceback (most recent call last):
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...
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KeyError: -1
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False
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>>> is_bipartite_bfs({-1: [0, 2], 0: [-1, 1], 1: [0, 2], 2: [-1, 1]})
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True
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>>> is_bipartite_bfs({0.9: [1, 3], 1: [0, 2], 2: [1, 3], 3: [0, 2]})
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Traceback (most recent call last):
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...
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KeyError: 0
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True
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>>> # FIXME: This test should fails with
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>>> # TypeError: list indices must be integers or...
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>>> is_bipartite_bfs({0: [1.0, 3.0], 1.0: [0, 2.0], 2.0: [1.0, 3.0], 3.0: [0, 2.0]})
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True
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>>> is_bipartite_bfs({"a": [1, 3], "b": [0, 2], "c": [1, 3], "d": [0, 2]})
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Traceback (most recent call last):
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...
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KeyError: 1
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True
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>>> is_bipartite_bfs({0: ["b", "d"], 1: ["a", "c"], 2: ["b", "d"], 3: ["a", "c"]})
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Traceback (most recent call last):
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...
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KeyError: 'b'
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True
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"""
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visited: defaultdict[int, int] = defaultdict(lambda: -1)
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for node in graph:
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@@ -164,6 +140,8 @@ def is_bipartite_bfs(graph: defaultdict[int, list[int]]) -> bool:
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visited[node] = 0
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while queue:
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curr_node = queue.popleft()
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if curr_node not in graph:
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continue
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for neighbor in graph[curr_node]:
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if visited[neighbor] == -1:
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visited[neighbor] = 1 - visited[curr_node]
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@@ -173,7 +151,7 @@ def is_bipartite_bfs(graph: defaultdict[int, list[int]]) -> bool:
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return True
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if __name__ == "__main":
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if __name__ == "__main__":
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import doctest
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result = doctest.testmod()
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