[C++] Knuth–Morris–Pratt (KMP) Algorithm (String Matching) 🔡

C++/README.md

@@ -46,4 +46,5 @@
 * Selection Sort
 
 ## String Algorithms
+* Knuth–Morris–Pratt _(KMP)_ Algorithm
 * Rabin-Karp Algorithm

C++/string_algorithms/CMakeLists.txt

@@ -1,4 +1,6 @@
 target_sources(programming
     PRIVATE
+    kmp_matcher.h
+    kmp_matcher.cpp
     rabin_karp_matcher.h
     rabin_karp_matcher.cpp)

C++/string_algorithms/kmp_matcher.cpp

@@ -0,0 +1,63 @@
+// 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 "kmp_matcher.h"
+
+#include <cmath>
+#include <string>
+#include <vector>
+
+namespace mehara::string {
+
+std::vector<int> compute_prefix_function(const std::string& pattern)
+{
+    int m = pattern.size();
+    std::vector<int> pi(m);
+    int k = 0;
+    for (int q = 1; q < m; q++) {
+        while (k > 0 && pattern[k] != pattern[q]) {
+            k = pi[k - 1];
+        }
+        if (pattern[k] == pattern[q]) {
+            k++;
+        }
+        pi[q] = k;
+    }
+    return pi;
+}
+
+std::vector<int> kmp_matcher(const std::string& text,
+                             const std::string& pattern)
+{
+    std::vector<int> matches;
+    int n = text.size();
+    int m = pattern.size();
+    auto pi = compute_prefix_function(pattern);
+    int q = 0;
+    for (int i = 0; i < n; i++) {
+        while (q > 0 && pattern[q] != text[i]) {
+            q = pi[q - 1];
+        }
+        if (pattern[q] == text[i]) {
+            q++;
+        }
+        if (q == m) {
+            matches.push_back(i - m + 1);
+            q = pi[q - 1];
+        }
+    }
+    return matches;
+}
+
+} // namespace mehara::string

C++/string_algorithms/kmp_matcher.h

@@ -0,0 +1,28 @@
+// 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_KMP_MATCHER_H_
+#define MEHARA_KMP_MATCHER_H_
+
+#include <string>
+#include <vector>
+
+namespace mehara::string {
+
+std::vector<int> kmp_matcher(const std::string& text,
+                             const std::string& pattern);
+
+} // namespace mehara::string
+
+#endif // MEHARA_KMP_MATCHER_H_