DFS implemented (#253)

Author: HarsheetKakar

pydatastructs/graphs/__init__.py

@@ -12,7 +12,8 @@
     breadth_first_search_parallel,
     minimum_spanning_tree,
     minimum_spanning_tree_parallel,
-    strongly_connected_components
+    strongly_connected_components,
+    depth_first_search
 )
 
 __all__.extend(algorithms.__all__)

pydatastructs/graphs/algorithms.py

@@ -2,7 +2,7 @@
 Contains all the algorithms associated with graph
 data structure.
 """
-from collections import deque as Queue
+from collections import deque
 from concurrent.futures import ThreadPoolExecutor
 from pydatastructs.utils import GraphEdge
 from pydatastructs.utils.misc_util import _comp
@@ -16,9 +16,12 @@
     'breadth_first_search_parallel',
     'minimum_spanning_tree',
     'minimum_spanning_tree_parallel',
-    'strongly_connected_components'
+    'strongly_connected_components',
+    'depth_first_search'
 ]
 
+Stack = Queue = deque
+
 def breadth_first_search(
     graph, source_node, operation, *args, **kwargs):
     """
@@ -548,3 +551,89 @@ def strongly_connected_components(graph, algorithm):
         "isn't implemented for finding strongly connected components."
         %(algorithm, graph._impl))
     return getattr(algorithms, func)(graph)
+
+def depth_first_search(
+    graph, source_node, operation, *args, **kwargs):
+    """
+    Implementation of depth first search (DFS)
+    algorithm.
+
+    Parameters
+    ==========
+
+    graph: Graph
+        The graph on which DFS is to be performed.
+    source_node: str
+        The name of the source node from where the DFS 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 depth_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)
+    >>> depth_first_search(G, V1.name, f, V3.name)
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Depth-first_search
+    """
+    import pydatastructs.graphs.algorithms as algorithms
+    func = "_depth_first_search_" + graph._impl
+    if not hasattr(algorithms, func):
+        raise NotImplementedError(
+        "Currently depth first search isn't implemented for "
+        "%s graphs."%(graph._impl))
+    return getattr(algorithms, func)(
+           graph, source_node, operation, *args, **kwargs)
+
+def _depth_first_search_adjacency_list(
+    graph, source_node, operation, *args, **kwargs):
+    dfs_stack = Stack()
+    visited = dict()
+    dfs_stack.append(source_node)
+    visited[source_node] = True
+    while len(dfs_stack) != 0:
+        curr_node = dfs_stack.pop()
+        next_nodes = graph.neighbors(curr_node)
+        if len(next_nodes) != 0:
+            for next_node in next_nodes:
+                if next_node.name not in visited:
+                    status = operation(curr_node, next_node.name, *args, **kwargs)
+                    if not status:
+                        return None
+                    dfs_stack.append(next_node.name)
+                    visited[next_node.name] = True
+        else:
+            status = operation(curr_node, "", *args, **kwargs)
+            if not status:
+                return None
+
+_depth_first_search_adjacency_matrix = _depth_first_search_adjacency_list

pydatastructs/graphs/tests/test_algorithms.py

@@ -1,6 +1,7 @@
 from pydatastructs import (breadth_first_search, Graph,
 breadth_first_search_parallel, minimum_spanning_tree,
-minimum_spanning_tree_parallel, strongly_connected_components)
+minimum_spanning_tree_parallel, strongly_connected_components,
+depth_first_search)
 
 
 def test_breadth_first_search():
@@ -185,3 +186,75 @@ def _test_strongly_connected_components(func, ds, algorithm, *args):
     scc = strongly_connected_components
     _test_strongly_connected_components(scc, "List", "kosaraju")
     _test_strongly_connected_components(scc, "Matrix", "kosaraju")
+
+def test_depth_first_search():
+
+    def _test_depth_first_search(ds):
+        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)
+
+        edges = [
+            (V1.name, V2.name),
+            (V2.name, V3.name),
+            (V1.name, V3.name)
+        ]
+
+        for edge in edges:
+            G1.add_edge(*edge)
+
+        parent = dict()
+        def dfs_tree(curr_node, next_node, parent):
+            if next_node != "":
+                parent[next_node] = curr_node
+            return True
+
+        depth_first_search(G1, V1.name, dfs_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)
+
+        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()
+        depth_first_search(G2, V4.name, path_finder, V7.name, parent, path)
+        assert path == [V4.name, V5.name, V6.name, V7.name]
+
+    _test_depth_first_search("List")
+    _test_depth_first_search("Matrix")