Added Bipartite Algorithm

Signed-off-by: Hargun Kaur <[email protected]>

Author: hargunkaur286

pydatastructs/graphs/__init__.py

@@ -21,7 +21,8 @@
     all_pair_shortest_paths,
     topological_sort,
     topological_sort_parallel,
-    max_flow
+    max_flow,
+    is_bipartite
 )
 
 __all__.extend(algorithms.__all__)

pydatastructs/graphs/algorithms.py

@@ -23,7 +23,8 @@
     'all_pair_shortest_paths',
     'topological_sort',
     'topological_sort_parallel',
-    'max_flow'
+    'max_flow',
+    'is_bipartite'
 ]
 
 Stack = Queue = deque
@@ -1216,3 +1217,57 @@ def max_flow(graph, source, sink, algorithm='edmonds_karp', **kwargs):
         f"Currently {algorithm} algorithm isn't implemented for "
         "performing max flow on graphs.")
     return getattr(algorithms, func)(graph, source, sink)
+
+def is_bipartite(graph):
+    """
+    Determines whether the given undirected graph is bipartite using BFS.
+
+    Parameters
+    ==========
+    graph : Graph
+        An undirected graph instance.
+
+    Returns
+    =======
+    (bool, dict)
+        A tuple where the first element is True if the graph is bipartite and False otherwise.
+        The second element is a dictionary mapping each vertex (its name) to a color (0 or 1)
+        if the graph is bipartite; if not, the dictionary may be partially filled.
+
+    Examples
+    ========
+    >>> from pydatastructs import Graph, AdjacencyListGraphNode, is_bipartite
+    >>> v0 = AdjacencyListGraphNode(0)
+    >>> v1 = AdjacencyListGraphNode(1)
+    >>> v2 = AdjacencyListGraphNode(2)
+    >>> v3 = AdjacencyListGraphNode(3)
+    >>> graph = Graph(v0, v1, v2, v3, implementation='adjacency_list')
+    >>> graph.add_edge(v0.name, v1.name)
+    >>> graph.add_edge(v1.name, v2.name)
+    >>> graph.add_edge(v2.name, v3.name)
+    >>> graph.add_edge(v3.name, v0.name)
+    >>> is_bipartite(graph)
+    (True, {'0': 0, '1': 1, '2': 0, '3': 1})
+
+    References
+    ==========
+    .. [1] https://en.wikipedia.org/wiki/Bipartite_graph
+    """
+    from collections import deque
+    color = {}
+
+    for vertex in graph.vertices:
+        vertex_name = vertex.name if hasattr(vertex, "name") else vertex
+        if vertex_name not in color:
+            color[vertex_name] = 0
+            queue = deque([vertex_name])
+            while queue:
+                u = queue.popleft()
+                for neighbor in graph.neighbors(u):
+                    v = neighbor.name if hasattr(neighbor, "name") else neighbor
+                    if v not in color:
+                        color[v] = 1 - color[u]
+                        queue.append(v)
+                    elif color[v] == color[u]:
+                        return (False, color)
+    return (True, color)

pydatastructs/graphs/tests/test_algorithms.py

@@ -2,7 +2,7 @@
 breadth_first_search_parallel, minimum_spanning_tree,
 minimum_spanning_tree_parallel, strongly_connected_components,
 depth_first_search, shortest_paths,all_pair_shortest_paths, topological_sort,
-topological_sort_parallel, max_flow)
+topological_sort_parallel, max_flow, is_bipartite)
 from pydatastructs.utils.raises_util import raises
 
 def test_breadth_first_search():
@@ -448,3 +448,38 @@ def _test_max_flow(ds, algorithm):
     _test_max_flow("Matrix", "edmonds_karp")
     _test_max_flow("List", "dinic")
     _test_max_flow("Matrix", "dinic")
+
+def test_is_bipartite():
+    import pydatastructs.utils.misc_util as utils
+    def _test_bipartite(ds):
+        GraphNode = getattr(utils, "Adjacency" + ds + "GraphNode")
+        impl = 'adjacency_list' if ds == "List" else 'adjacency_matrix'
+
+        v0 = GraphNode(0)
+        v1 = GraphNode(1)
+        v2 = GraphNode(2)
+        v3 = GraphNode(3)
+        graph = Graph(v0, v1, v2, v3, implementation=impl)
+        graph.add_edge(v0.name, v1.name)
+        graph.add_edge(v1.name, v2.name)
+        graph.add_edge(v2.name, v3.name)
+        graph.add_edge(v3.name, v0.name)
+        bip, colors = is_bipartite(graph)
+        assert bip is True
+        assert colors[v0.name] != colors[v1.name]
+        assert colors[v1.name] != colors[v2.name]
+        assert colors[v2.name] != colors[v3.name]
+        assert colors[v3.name] != colors[v0.name]
+
+        u0 = GraphNode(0)
+        u1 = GraphNode(1)
+        u2 = GraphNode(2)
+        graph = Graph(u0, u1, u2, implementation=impl)
+        graph.add_edge(u0.name, u1.name)
+        graph.add_edge(u1.name, u2.name)
+        graph.add_edge(u2.name, u0.name)
+        bip, _ = is_bipartite(graph)
+        assert bip is False
+
+    _test_bipartite("List")
+    _test_bipartite("Matrix")