feat: Add C++ backend for strings module

- Implemented C++ backend for string algorithms (KMP, Rabin-Karp, Boyer-Moore, Z-function).
- Implemented C++ backend for Trie data structure.
- Added Python-C++ interface using `Python.h`.
- Updated `_extensions.py` and `setup.py` to integrate the new backend.

Author: asmit27rai

pydatastructs/strings/_backend/__init__.py

@@ -0,0 +1,143 @@
+#include "algorithms.hpp"
+#include <vector>
+#include <string>
+#include <unordered_map>
+#include <cmath>
+
+// Knuth-Morris-Pratt Algorithm
+std::vector<int> kmp_search(const std::string& text, const std::string& query) {
+    std::vector<int> positions;
+    if (text.empty() || query.empty()) return positions;
+
+    // Build KMP table
+    std::vector<int> kmp_table(query.size() + 1, 0);
+    kmp_table[0] = -1;
+    int pos = 1, cnd = 0;
+    while (pos < query.size()) {
+        if (query[pos] == query[cnd]) {
+            kmp_table[pos] = kmp_table[cnd];
+        } else {
+            kmp_table[pos] = cnd;
+            while (cnd >= 0 && query[pos] != query[cnd]) {
+                cnd = kmp_table[cnd];
+            }
+        }
+        pos++, cnd++;
+    }
+    kmp_table[pos] = cnd;
+
+    // Perform search
+    int j = 0, k = 0;
+    while (j < text.size()) {
+        if (query[k] == text[j]) {
+            j++, k++;
+            if (k == query.size()) {
+                positions.push_back(j - k);
+                k = kmp_table[k];
+            }
+        } else {
+            k = kmp_table[k];
+            if (k < 0) {
+                j++, k++;
+            }
+        }
+    }
+
+    return positions;
+}
+
+// Rabin-Karp Algorithm
+std::vector<int> rabin_karp_search(const std::string& text, const std::string& query) {
+    std::vector<int> positions;
+    if (text.empty() || query.empty()) return positions;
+
+    const int PRIME = 257;
+    const int MOD = 1000000007;
+    int t = text.size(), q = query.size();
+    long long query_hash = 0, text_hash = 0, power = 1;
+
+    // Precompute power
+    for (int i = 0; i < q - 1; i++) {
+        power = (power * PRIME) % MOD;
+    }
+
+    // Compute hash for query and first window of text
+    for (int i = 0; i < q; i++) {
+        query_hash = (query_hash * PRIME + query[i]) % MOD;
+        text_hash = (text_hash * PRIME + text[i]) % MOD;
+    }
+
+    // Slide the window over the text
+    for (int i = 0; i <= t - q; i++) {
+        if (query_hash == text_hash) {
+            if (text.substr(i, q) == query) {
+                positions.push_back(i);
+            }
+        }
+        if (i < t - q) {
+            text_hash = (PRIME * (text_hash - text[i] * power) + text[i + q]) % MOD;
+            if (text_hash < 0) text_hash += MOD;
+        }
+    }
+
+    return positions;
+}
+
+// Boyer-Moore Algorithm
+std::vector<int> boyer_moore_search(const std::string& text, const std::string& query) {
+    std::vector<int> positions;
+    if (text.empty() || query.empty()) return positions;
+
+    // Preprocessing
+    std::unordered_map<char, int> bad_match_table;
+    for (int i = 0; i < query.size(); i++) {
+        bad_match_table[query[i]] = i;
+    }
+
+    // Searching
+    int shift = 0;
+    while (shift <= text.size() - query.size()) {
+        int j = query.size() - 1;
+        while (j >= 0 && query[j] == text[shift + j]) {
+            j--;
+        }
+        if (j < 0) {
+            positions.push_back(shift);
+            shift += (shift + query.size() < text.size()) ? query.size() - bad_match_table[text[shift + query.size()]] : 1;
+        } else {
+            shift += std::max(1, j - bad_match_table[text[shift + j]]);
+        }
+    }
+
+    return positions;
+}
+
+// Z-Function Algorithm
+std::vector<int> z_function_search(const std::string& text, const std::string& query) {
+    std::vector<int> positions;
+    if (text.empty() || query.empty()) return positions;
+
+    std::string combined = query + "$" + text;
+    std::vector<int> z(combined.size(), 0);
+    int l = 0, r = 0;
+
+    for (int i = 1; i < combined.size(); i++) {
+        if (i <= r) {
+            z[i] = std::min(r - i + 1, z[i - l]);
+        }
+        while (i + z[i] < combined.size() && combined[z[i]] == combined[i + z[i]]) {
+            z[i]++;
+        }
+        if (i + z[i] - 1 > r) {
+            l = i, r = i + z[i] - 1;
+        }
+    }
+
+    for (int i = query.size() + 1; i < combined.size(); i++) {
+        if (z[i] == query.size()) {
+            positions.push_back(i - query.size() - 1);
+        }
+    }
+
+    return positions;
+}

pydatastructs/strings/_backend/cpp/algorithms/algorithms.cpp

@@ -0,0 +1,22 @@
+#ifndef STRINGS_ALGORITHMS_HPP
+#define STRINGS_ALGORITHMS_HPP
+
+#include <Python.h>
+#include <vector>
+#include <string>
+#include <unordered_map>
+#include <cmath>
+
+// Knuth-Morris-Pratt Algorithm
+std::vector<int> kmp_search(const std::string& text, const std::string& query);
+
+// Rabin-Karp Algorithm
+std::vector<int> rabin_karp_search(const std::string& text, const std::string& query);
+
+// Boyer-Moore Algorithm
+std::vector<int> boyer_moore_search(const std::string& text, const std::string& query);
+
+// Z-Function Algorithm
+std::vector<int> z_function_search(const std::string& text, const std::string& query);
+
+#endif

pydatastructs/strings/_backend/cpp/algorithms/algorithms.hpp

@@ -0,0 +1,75 @@
+#include <Python.h>
+#include "algorithms/algorithms.hpp"
+#include "trie/trie.hpp"
+#include "utils/_backend/cpp/string.hpp"
+
+// Python wrapper for KMP algorithm
+static PyObject* py_kmp_search(PyObject* self, PyObject* args) {
+    PyObject *text_obj, *query_obj;
+    if (!PyArg_ParseTuple(args, "OO", &text_obj, &query_obj)) {
+        return NULL;
+    }
+    std::string text = pyobj_to_string(text_obj);
+    std::string query = pyobj_to_string(query_obj);
+    std::vector<int> positions = kmp_search(text, query);
+    return vector_to_pylist(positions);
+}
+
+// Python wrapper for Rabin-Karp algorithm
+static PyObject* py_rabin_karp_search(PyObject* self, PyObject* args) {
+    PyObject *text_obj, *query_obj;
+    if (!PyArg_ParseTuple(args, "OO", &text_obj, &query_obj)) {
+        return NULL;
+    }
+    std::string text = pyobj_to_string(text_obj);
+    std::string query = pyobj_to_string(query_obj);
+    std::vector<int> positions = rabin_karp_search(text, query);
+    return vector_to_pylist(positions);
+}
+
+// Python wrapper for Boyer-Moore algorithm
+static PyObject* py_boyer_moore_search(PyObject* self, PyObject* args) {
+    PyObject *text_obj, *query_obj;
+    if (!PyArg_ParseTuple(args, "OO", &text_obj, &query_obj)) {
+        return NULL;
+    }
+    std::string text = pyobj_to_string(text_obj);
+    std::string query = pyobj_to_string(query_obj);
+    std::vector<int> positions = boyer_moore_search(text, query);
+    return vector_to_pylist(positions);
+}
+
+// Python wrapper for Z-function algorithm
+static PyObject* py_z_function_search(PyObject* self, PyObject* args) {
+    PyObject *text_obj, *query_obj;
+    if (!PyArg_ParseTuple(args, "OO", &text_obj, &query_obj)) {
+        return NULL;
+    }
+    std::string text = pyobj_to_string(text_obj);
+    std::string query = pyobj_to_string(query_obj);
+    std::vector<int> positions = z_function_search(text, query);
+    return vector_to_pylist(positions);
+}
+
+// Define the module's method table
+static PyMethodDef StringsMethods[] = {
+    {"kmp_search", py_kmp_search, METH_VARARGS, "Perform KMP search"},
+    {"rabin_karp_search", py_rabin_karp_search, METH_VARARGS, "Perform Rabin-Karp search"},
+    {"boyer_moore_search", py_boyer_moore_search, METH_VARARGS, "Perform Boyer-Moore search"},
+    {"z_function_search", py_z_function_search, METH_VARARGS, "Perform Z-function search"},
+    {NULL, NULL, 0, NULL}
+};
+
+// Define the module
+static struct PyModuleDef stringsmodule = {
+    PyModuleDef_HEAD_INIT,
+    "_strings",
+    NULL,
+    -1,
+    StringsMethods
+};
+
+// Module initialization function
+PyMODINIT_FUNC PyInit__strings(void) {
+    return PyModule_Create(&stringsmodule);
+}

pydatastructs/strings/_backend/cpp/string.cpp

@@ -0,0 +1,73 @@
+#include "trie.hpp"
+
+TrieNode::~TrieNode() {
+    for (auto& pair : children) {
+        delete pair.second;
+    }
+}
+
+Trie::Trie() {
+    root = new TrieNode();
+}
+
+Trie::~Trie() {
+    delete root;
+}
+
+void Trie::insert(const std::string& word) {
+    TrieNode* current = root;
+    for (char ch : word) {
+        if (current->children.find(ch) == current->children.end()) {
+            current->children[ch] = new TrieNode(ch);
+        }
+        current = current->children[ch];
+    }
+    current->is_terminal = true;
+}
+
+bool Trie::search(const std::string& word) {
+    TrieNode* current = root;
+    for (char ch : word) {
+        if (current->children.find(ch) == current->children.end()) {
+            return false;
+        }
+        current = current->children[ch];
+    }
+    return current->is_terminal;
+}
+
+bool Trie::starts_with(const std::string& prefix) {
+    TrieNode* current = root;
+    for (char ch : prefix) {
+        if (current->children.find(ch) == current->children.end()) {
+            return false;
+        }
+        current = current->children[ch];
+    }
+    return true;
+}
+
+std::vector<std::string> Trie::strings_with_prefix(const std::string& prefix) {
+    std::vector<std::string> result;
+    TrieNode* current = root;
+    for (char ch : prefix) {
+        if (current->children.find(ch) == current->children.end()) {
+            return result;
+        }
+        current = current->children[ch];
+    }
+    // Perform DFS to collect all strings with the given prefix
+    std::vector<std::pair<TrieNode*, std::string>> stack;
+    stack.push_back({current, prefix});
+    while (!stack.empty()) {
+        auto [node, str] = stack.back();
+        stack.pop_back();
+        if (node->is_terminal) {
+            result.push_back(str);
+        }
+        for (auto& pair : node->children) {
+            stack.push_back({pair.second, str + pair.first});
+        }
+    }
+    return result;
+}

pydatastructs/strings/_backend/cpp/trie/trie.cpp

@@ -0,0 +1,32 @@
+#ifndef STRINGS_TRIE_HPP
+#define STRINGS_TRIE_HPP
+
+#include <Python.h>
+#include <unordered_map>
+#include <vector>
+#include <string>
+
+class TrieNode {
+public:
+    char character;
+    bool is_terminal;
+    std::unordered_map<char, TrieNode*> children;
+
+    TrieNode(char ch = '\0') : character(ch), is_terminal(false) {}
+    ~TrieNode();
+};
+
+class Trie {
+public:
+    TrieNode* root;
+
+    Trie();
+    ~Trie();
+
+    void insert(const std::string& word);
+    bool search(const std::string& word);
+    bool starts_with(const std::string& prefix);
+    std::vector<std::string> strings_with_prefix(const std::string& prefix);
+};
+
+#endif

pydatastructs/strings/_backend/cpp/trie/trie.hpp

@@ -0,0 +1,35 @@
+from setuptools import Extension
+
+project = 'pydatastructs'
+
+module = 'strings'
+
+backend = '_backend'
+
+cpp = 'cpp'
+
+# Define the extension for string algorithms
+algorithms = '.'.join([project, module, backend, cpp, '_algorithms'])
+algorithms_sources = [
+    '/'.join([project, module, backend, cpp, 'algorithms', 'algorithms.cpp']),
+    '/'.join([project, "utils", "_backend", "cpp", "string.cpp"])
+]
+
+# Define the extension for the Trie data structure
+trie = '.'.join([project, module, backend, cpp, '_trie'])
+trie_sources = [
+    '/'.join([project, module, backend, cpp, 'trie', 'trie.cpp']),
+    '/'.join([project, "utils", "_backend", "cpp", "string.cpp"])
+]
+
+# Define the extension for the main strings module
+strings = '.'.join([project, module, backend, cpp, '_strings'])
+strings_sources = [
+    '/'.join([project, module, backend, cpp, 'strings.cpp'])
+]
+
+extensions = [
+    Extension(algorithms, sources=algorithms_sources),
+    Extension(trie, sources=trie_sources),
+    Extension(strings, sources=strings_sources)
+]