Add KMP string matching algorithm (#2719)

strings/kmp_string_matching.cpp

@@ -0,0 +1,61 @@
+/**
+ * @file kmp_string_matching.cpp
+ * @brief Implementation of the Knuth-Morris-Pratt (KMP) string matching algorithm
+ *
+ * @details
+ * The KMP algorithm improves the naive string matching method by avoiding unnecessary rechecking of characters.
+ * It uses a precomputed Longest Prefix Suffix (LPS) array to efficiently search for a pattern in a given text.
+ *
+ * Time Complexity: O(n + m), where n = length of text, m = length of pattern.
+ * Space Complexity: O(m), for the LPS array.
+ *
+ * @author YashAstro11
+ * @date 2025-04-13
+ */
+
+#include <iostream>
+#include <vector>
+using namespace std;
+
+vector<int> computeLPS(const string& pattern) {
+    int n = pattern.length();
+    vector<int> lps(n, 0);
+    int len = 0;
+
+    for (int i = 1; i < n; ) {
+        if (pattern[i] == pattern[len]) {
+            lps[i++] = ++len;
+        } else if (len != 0) {
+            len = lps[len - 1];
+        } else {
+            lps[i++] = 0;
+        }
+    }
+    return lps;
+}
+
+void KMPSearch(const string& text, const string& pattern) {
+    vector<int> lps = computeLPS(pattern);
+    int i = 0, j = 0;
+    int n = text.length(), m = pattern.length();
+
+    while (i < n) {
+        if (pattern[j] == text[i]) {
+            i++, j++;
+        }
+
+        if (j == m) {
+            cout << "Pattern found at index " << i - j << endl;
+            j = lps[j - 1];
+        } else if (i < n && pattern[j] != text[i]) {
+            j = (j != 0) ? lps[j - 1] : 0;
+        }
+    }
+}
+
+int main() {
+    string text = "ababcabcabababd";
+    string pattern = "ababd";
+    KMPSearch(text, pattern);
+    return 0;
+}