Implement C++ Backend for Breadth-First Search

docs/source/pydatastructs/graphs/algorithms.rst

@@ -21,4 +21,6 @@ Algorithms
 
 .. autofunction:: pydatastructs.topological_sort_parallel
 
-.. autofunction:: pydatastructs.find_bridges
+.. autofunction:: pydatastructs.find_bridges
+
+.. autofunction:: pydatastructs.bfs

pydatastructs/graphs/__init__.py

@@ -1,6 +1,11 @@
-__all__ = []
+__all__ = [
+    'bfs'
+    ]
 
-from . import graph
+from . import (
+    graph,
+    _extensions
+)
 from .graph import (
     Graph
 )
@@ -22,7 +27,8 @@
     topological_sort,
     topological_sort_parallel,
     max_flow,
-    find_bridges
+    find_bridges,
+    bfs
 )
 
 __all__.extend(algorithms.__all__)

pydatastructs/graphs/_backend/cpp/algorithms.cpp

@@ -0,0 +1,21 @@
+#include <Python.h>
+#include "bfs.hpp"
+
+static PyMethodDef bfs_PyMethodDef[] = {
+    {"bfs", (PyCFunction)bfs, METH_VARARGS | METH_KEYWORDS, "Breadth-First Search"},
+    {NULL, NULL, 0, NULL}
+};
+
+static struct PyModuleDef bfs_module = {
+    PyModuleDef_HEAD_INIT,
+    "_bfs",
+    "BFS algorithms module",
+    -1,
+    bfs_PyMethodDef
+};
+
+PyMODINIT_FUNC PyInit__bfs(void) {
+    PyObject *module = PyModule_Create(&bfs_module);
+    if (module == NULL) return NULL;
+    return module;
+}

pydatastructs/graphs/_backend/cpp/bfs.hpp

@@ -0,0 +1,64 @@
+#ifndef BFS_HPP
+#define BFS_HPP
+
+#define PY_SSIZE_T_CLEAN
+#include <Python.h>
+#include <queue>
+#include <unordered_map>
+
+struct Graph {
+    PyObject* adj_list;
+};
+
+static PyObject* bfs_impl(PyObject* graph, PyObject* start_vertex, PyObject* visited = NULL) {
+    if (!PyDict_Check(graph)) {
+        PyErr_SetString(PyExc_TypeError, "Graph must be a dictionary");
+        return NULL;
+    }
+
+    std::queue<PyObject*> q;
+    PyObject* visited_dict = visited ? visited : PyDict_New();
+
+    q.push(start_vertex);
+    PyDict_SetItem(visited_dict, start_vertex, Py_True);
+
+    PyObject* result = PyList_New(0);
+
+    while (!q.empty()) {
+        PyObject* vertex = q.front();
+        q.pop();
+
+        PyList_Append(result, vertex);
+
+        PyObject* neighbors = PyDict_GetItem(graph, vertex);
+        if (neighbors && PyList_Check(neighbors)) {
+            Py_ssize_t size = PyList_Size(neighbors);
+            for (Py_ssize_t i = 0; i < size; i++) {
+                PyObject* neighbor = PyList_GetItem(neighbors, i);
+                if (!PyDict_Contains(visited_dict, neighbor)) {
+                    q.push(neighbor);
+                    PyDict_SetItem(visited_dict, neighbor, Py_True);
+                }
+            }
+        }
+    }
+
+    if (!visited) Py_DECREF(visited_dict);
+    return result;
+}
+
+static PyObject* bfs(PyObject* self, PyObject* args, PyObject* kwds) {
+    PyObject *graph = NULL, *start_vertex = NULL;
+    static char *kwlist[] = {"graph", "start_vertex", NULL};
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "OO", kwlist, &graph, &start_vertex)) {
+        return NULL;
+    }
+
+    PyObject* result = bfs_impl(graph, start_vertex);
+    if (result == NULL) return NULL;
+    Py_INCREF(result);
+    return result;
+}
+
+#endif

pydatastructs/graphs/_extensions.py

@@ -0,0 +1,17 @@
+from setuptools import Extension
+import sysconfig
+
+project = 'pydatastructs'
+
+module = 'graphs'
+
+backend = "_backend"
+
+cpp = 'cpp'
+
+bfs = '.'.join([project, module, backend, cpp, '_bfs'])
+bfs_sources = ['/'.join([project, module, backend, cpp, 'algorithms.cpp'])]
+
+extensions = [
+    Extension(bfs, sources=bfs_sources)
+]

pydatastructs/graphs/algorithms.py

@@ -11,6 +11,7 @@
 from pydatastructs.graphs.graph import Graph
 from pydatastructs.linear_data_structures.algorithms import merge_sort_parallel
 from pydatastructs import PriorityQueue
+from pydatastructs.graphs._backend.cpp._bfs import bfs as _bfs_cpp
 
 __all__ = [
     'breadth_first_search',
@@ -24,7 +25,8 @@
     'topological_sort',
     'topological_sort_parallel',
     'max_flow',
-    'find_bridges'
+    'find_bridges',
+    'bfs'
 ]
 
 Stack = Queue = deque
@@ -1368,3 +1370,18 @@ def dfs(u):
             bridges.append((b, a))
     bridges.sort()
     return bridges
+
+def bfs(graph, start_vertex, backend=Backend.PYTHON):
+    if backend == Backend.CPP:
+        return _bfs_cpp(graph, start_vertex)
+    from collections import deque
+    visited = set()
+    q = deque([start_vertex])
+    result = []
+    while q:
+        vertex = q.popleft()
+        if vertex not in visited:
+            visited.add(vertex)
+            result.append(vertex)
+            q.extend(graph.get(vertex, []))
+    return result

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, find_bridges)
+topological_sort_parallel, max_flow, find_bridges, bfs, Backend)
 from pydatastructs.utils.raises_util import raises
 
 def test_breadth_first_search():
@@ -504,3 +504,20 @@ def _test_find_bridges(ds):
 
     _test_find_bridges("List")
     _test_find_bridges("Matrix")
+
+def test_bfs():
+    graph = {
+        0: [1, 2],
+        1: [0, 3],
+        2: [0],
+        3: [1]
+    }
+    start_vertex = 0
+    expected = [0, 1, 2, 3]
+
+    result_python = bfs(graph, start_vertex, backend=Backend.PYTHON)
+    assert result_python == expected
+
+    result_cpp = bfs(graph, start_vertex, backend=Backend.CPP)
+    result_cpp_list = [x for x in result_cpp]
+    assert result_cpp_list == expected

setup.py

@@ -3,6 +3,7 @@
 from pydatastructs import linear_data_structures
 from pydatastructs import miscellaneous_data_structures
 from pydatastructs import trees
+from pydatastructs import graphs
 
 with open("README.md", "r") as fh:
     long_description = fh.read()
@@ -13,6 +14,7 @@
 extensions.extend(linear_data_structures._extensions.extensions)
 extensions.extend(miscellaneous_data_structures._extensions.extensions)
 extensions.extend(trees._extensions.extensions)
+extensions.extend(graphs._extensions.extensions)
 
 setuptools.setup(
     name="cz-pydatastructs",