[C++] Rabin-Karp Algorithm (String Matching) 🔡

C++/CMakeLists.txt

@@ -22,4 +22,5 @@ add_subdirectory(mathematics)
 add_subdirectory(randomized_algorithms)
 add_subdirectory(search)
 add_subdirectory(sort)
+add_subdirectory(string_algorithms)
 add_subdirectory(test)

C++/README.md

@@ -44,3 +44,6 @@
 * Merge Sort
 * Quick Sort
 * Selection Sort
+
+## String Algorithms
+* Rabin-Karp Algorithm

C++/string_algorithms/CMakeLists.txt

@@ -0,0 +1,4 @@
+target_sources(programming
+    PRIVATE
+    rabin_karp_matcher.h
+    rabin_karp_matcher.cpp)

C++/string_algorithms/rabin_karp_matcher.cpp

@@ -0,0 +1,62 @@
+// Copyright 2024 Aman Mehara
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "rabin_karp_matcher.h"
+#include "../mathematics/number_theory/exponentiation.h"
+
+#include <cmath>
+#include <string>
+#include <vector>
+
+namespace mehara::string {
+
+std::vector<int> rabin_karp_matcher(const std::string& text,
+                                    const std::string& pattern, int radix,
+                                    int prime)
+{
+    std::vector<int> matches;
+    int n = text.size();
+    int m = pattern.size();
+    int h = mathematics::modular_exponentiation(radix, m - 1, prime);
+    int pattern_hash = 0;
+    int rolling_hash = 0;
+    for (int i = 0; i < m; i++) {
+        pattern_hash = (radix * pattern_hash + pattern[i]) % prime;
+        rolling_hash = (radix * rolling_hash + text[i]) % prime;
+    }
+    for (int i = 0; i <= n - m; i++) {
+        if (pattern_hash == rolling_hash) {
+            bool match = true;
+            for (int j = 0; j < m; j++) {
+                if (pattern[j] != text[i + j]) {
+                    match = false;
+                    break;
+                }
+            }
+            if (match) {
+                matches.push_back(i);
+            }
+        }
+        if (i < n - m) {
+            rolling_hash =
+                (radix * (rolling_hash - text[i] * h) + text[i + m]) % prime;
+            if (rolling_hash < 0) {
+                rolling_hash += prime;
+            }
+        }
+    }
+    return matches;
+}
+
+} // namespace mehara::string

C++/string_algorithms/rabin_karp_matcher.h

@@ -0,0 +1,29 @@
+// Copyright 2024 Aman Mehara
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef MEHARA_RABIN_KARP_H_
+#define MEHARA_RABIN_KARP_H_
+
+#include <string>
+#include <vector>
+
+namespace mehara::string {
+
+std::vector<int> rabin_karp_matcher(const std::string& text,
+                                    const std::string& pattern, int radix,
+                                    int prime);
+
+} // namespace mehara::string
+
+#endif // MEHARA_RABIN_KARP_H_