Added Rabin Karp String Matching in c++ (#1156)

Rabin_Karp/Rabin_Karp.cpp

@@ -0,0 +1,74 @@
+// Rabin Karp Algorithm
+/*
+AN : range or No of alphabets
+val : AN ^ patlen-1
+patlen : pattern length
+PN: any prime no given input from main
+*/
+
+/* Time-Complexity:-
+The average case running time of the Rabin-Karp algorithm = O(n+m).
+The best case running time of the Rabin-Karp algorithm = O(n+m).
+The worst-case running time of the Rabin-Karp algorithm = O(nm).
+*/
+
+#include<iostream>
+#include<cstring>
+#define AN 256    // no. of character in alphabet
+using namespace std;
+
+void search(char *pattern, char *text, int PN)
+{
+    int patlen = strlen(pattern);   // pattern length
+    int txtlen = strlen(text);      // text length
+    int val = 1;
+    int hpat = 0;      // pattern hash value
+    int htxt = 0;      // text hash value
+    int i, j;
+    for (i = 0; i < patlen - 1; i++)
+         val = (val * AN) % PN;       // PN is a prime number
+    for (i = 0; i < patlen; i++)
+    {
+         hpat = (AN * hpat + pattern[i]) % PN;
+         htxt = (AN * htxt + text[i]) % PN;
+    }
+    for (i = 0; i <= txtlen - patlen; i++)
+    {
+         if ( hpat == htxt )
+         {
+            // Check for patterns
+             for (j = 0; j < patlen; j++)
+             {
+                 if (text[i + j] != pattern[j])
+                 {
+                    break;
+                 }
+            }
+            if (j == patlen)
+            {
+                cout << "Found at index starting from " << i << endl;
+            }
+        }
+        // Calculate the new pattern including i+m
+        htxt = (AN * (htxt - val * text[i]) + text[i + patlen]) % PN;
+        if (htxt < 0)
+        {
+            htxt = htxt + PN;
+        }
+    }
+}
+
+int main() {
+    char *text = "XWINGO XOR WINGO";
+    char *pattern = "WINGO";
+    int PN = 101;  // A prime number
+    search(pattern, text, PN);
+    return 0;
+}
+
+/* Input:-XWINGO XOR WINGO
+         WINGO
+         101
+ OUTPUT:-Found at index starting from 1
+         Found at index starting from 11
+*/