Added Serial BFS (#126)

Author: czgdp1807

pydatastructs/__init__.py

@@ -2,3 +2,4 @@
 from .trees import *
 from .miscellaneous_data_structures import *
 from .utils import *
+from .graphs import *

pydatastructs/graphs/__init__.py

@@ -5,3 +5,10 @@
     Graph
 )
 __all__.extend(graph.__all__)
+
+from . import algorithms
+from .algorithms import (
+    breadth_first_search
+)
+
+__all__.extend(algorithms.__all__)

pydatastructs/graphs/algorithms.py

@@ -0,0 +1,92 @@
+"""
+Contains all the algorithms associated with graph
+data structure.
+"""
+# TODO: REPLACE COLLECTIONS QUEUE WITH PYDATASTRUCTS QUEUE
+from collections import deque as Queue
+from pydatastructs.utils.misc_util import AdjacencyListGraphNode
+
+__all__ = [
+    'breadth_first_search',
+]
+
+def breadth_first_search(
+    graph, source_node, operation, *args, **kwargs):
+    """
+    Implementation of serial breadth first search(BFS)
+    algorithm.
+
+    Parameters
+    ==========
+
+    graph: Graph
+        The graph on which BFS is to be performed.
+    source_node: str
+        The name of the source node from where the BFS is
+        to be initiated.
+    operation: function
+        The function which is to be applied
+        on every node when it is visited.
+        The prototype which is to be followed is,
+        `function_name(curr_node, next_node,
+                       arg_1, arg_2, . . ., arg_n)`.
+        Here, the first two arguments denote, the
+        current node and the node next to current node.
+        The rest of the arguments are optional and you can
+        provide your own stuff there.
+
+    Note
+    ====
+
+    You should pass all the arguments which you are going
+    to use in the prototype of your `operation` after
+    passing the operation function.
+
+    Examples
+    ========
+
+    >>> from pydatastructs import Graph, AdjacencyListGraphNode
+    >>> V1 = AdjacencyListGraphNode("V1")
+    >>> V2 = AdjacencyListGraphNode("V2")
+    >>> V3 = AdjacencyListGraphNode("V3")
+    >>> G = Graph(V1, V2, V3)
+    >>> from pydatastructs import breadth_first_search
+    >>> def f(curr_node, next_node, dest_node):
+    ...     return curr_node != dest_node
+    ...
+    >>> G.add_edge(V1.name, V2.name)
+    >>> G.add_edge(V2.name, V3.name)
+    >>> breadth_first_search(G, V1.name, f, V3.name)
+    """
+    import pydatastructs.graphs.algorithms as algorithms
+    func = "_breadth_first_search_" + graph._impl
+    if not hasattr(algorithms, func):
+        raise NotImplementedError(
+        "Currently breadth first search isn't implemented for "
+        "%s graphs."%(graph._impl))
+    return getattr(algorithms, func)(
+           graph, source_node, operation, *args, **kwargs)
+
+def _breadth_first_search_adjacency_list(
+    graph, source_node, operation, *args, **kwargs):
+    bfs_queue = Queue()
+    visited = dict()
+    bfs_queue.append(source_node)
+    visited[source_node] = True
+    while len(bfs_queue) != 0:
+        curr_node = bfs_queue.popleft()
+        next_nodes = graph.neighbors(curr_node)
+        if len(next_nodes) != 0:
+            for next_node in next_nodes:
+                if visited.get(next_node.name, False) is False:
+                    status = operation(curr_node, next_node.name, *args, **kwargs)
+                    if not status:
+                        return None
+                    bfs_queue.append(next_node.name)
+                    visited[next_node.name] = True
+        else:
+            status = operation(curr_node, "", *args, **kwargs)
+            if not status:
+                return None
+
+_breadth_first_search_adjacency_matrix = _breadth_first_search_adjacency_list

pydatastructs/graphs/graph.py

@@ -43,14 +43,21 @@ class Graph(object):
 
     .. [1] https://en.wikipedia.org/wiki/Graph_(abstract_data_type)
     """
+
+    __slots__ = ['_impl']
+
     def __new__(cls, *args, **kwargs):
         implementation = kwargs.get('implementation', 'adjacency_list')
         if implementation is 'adjacency_list':
             from pydatastructs.graphs.adjacency_list import AdjacencyList
-            return AdjacencyList(*args)
+            obj = AdjacencyList(*args)
+            obj._impl = implementation
+            return obj
         elif implementation is 'adjacency_matrix':
             from pydatastructs.graphs.adjacency_matrix import AdjacencyMatrix
-            return AdjacencyMatrix(*args)
+            obj = AdjacencyMatrix(*args)
+            obj._impl = implementation
+            return obj
         else:
             raise NotImplementedError("%s implementation is not a part "
                                       "of the library currently."%(implementation))

pydatastructs/graphs/tests/test_algorithms.py

@@ -0,0 +1,74 @@
+from pydatastructs import breadth_first_search, Graph
+
+
+def test_breadth_first_search():
+
+    def _test_breadth_first_search(ds, impl):
+        import pydatastructs.utils.misc_util as utils
+        GraphNode = getattr(utils, "Adjacency" + ds + "GraphNode")
+
+        V1 = GraphNode(0)
+        V2 = GraphNode(1)
+        V3 = GraphNode(2)
+
+        G1 = Graph(V1, V2, V3, implementation=impl)
+
+        edges = [
+            (V1.name, V2.name),
+            (V2.name, V3.name),
+            (V1.name, V3.name)
+        ]
+
+        for edge in edges:
+            G1.add_edge(*edge)
+
+        parent = dict()
+        def bfs_tree(curr_node, next_node, parent):
+            if next_node != "":
+                parent[next_node] = curr_node
+            return True
+
+        breadth_first_search(G1, V1.name, bfs_tree, parent)
+        assert (parent[V3.name] == V1.name and parent[V2.name] == V1.name) or \
+            (parent[V3.name] == V2.name and parent[V2.name] == V1.name)
+
+        V4 = GraphNode(0)
+        V5 = GraphNode(1)
+        V6 = GraphNode(2)
+        V7 = GraphNode(3)
+        V8 = GraphNode(4)
+
+        edges = [
+            (V4.name, V5.name),
+            (V5.name, V6.name),
+            (V6.name, V7.name),
+            (V6.name, V4.name),
+            (V7.name, V8.name)
+        ]
+
+        G2 = Graph(V4, V5, V6, V7, V8, implementation=impl)
+
+        for edge in edges:
+            G2.add_edge(*edge)
+
+        path = []
+        def path_finder(curr_node, next_node, dest_node, parent, path):
+            if next_node != "":
+                parent[next_node] = curr_node
+            if curr_node == dest_node:
+                node = curr_node
+                path.append(node)
+                while node is not None:
+                    if parent.get(node, None) is not None:
+                        path.append(parent[node])
+                    node = parent.get(node, None)
+                path.reverse()
+                return False
+            return True
+
+        parent.clear()
+        breadth_first_search(G2, V4.name, path_finder, V7.name, parent, path)
+        assert path == [V4.name, V5.name, V6.name, V7.name]
+
+    _test_breadth_first_search("List", "adjacency_list")
+    _test_breadth_first_search("Matrix", "adjacency_matrix")

pydatastructs/utils/misc_util.py

@@ -150,9 +150,9 @@ class AdjacencyListGraphNode(GraphNode):
         nodes of the current node.
         Optional, by default, None
     """
-    def __new__(cls, name, data, adjacency_list=None):
+    def __new__(cls, name, data=None, adjacency_list=None):
         obj = GraphNode.__new__(cls)
-        obj.name, obj.data = name, data
+        obj.name, obj.data = str(name), data
         if adjacency_list is not None:
             for node in adjacency_list:
                 obj.__setattr__(node.name, node)
@@ -197,10 +197,10 @@ class AdjacencyMatrixGraphNode(GraphNode):
     """
     __slots__ = ['name', 'data']
 
-    def __new__(cls, name, data):
+    def __new__(cls, name, data=None):
         obj = GraphNode.__new__(cls)
         obj.name, obj.data, obj.is_connected = \
-            name, data, None
+            int(name), data, None
         return obj
 
 class GraphEdge(object):