Create Rabin-Karp Algorithm

Rabin-Karp Algorithm

@@ -0,0 +1,79 @@
+#include <bits/stdc++.h> 
+using namespace std; 
+
+// d is the number of characters in the input alphabet  
+#define d 256  
+
+/* pat -> pattern  
+    txt -> text  
+    q -> A prime number  
+*/
+void search(char pat[], char txt[], int q)  
+{  
+    int M = strlen(pat);  
+    int N = strlen(txt);  
+    int i, j;  
+    int p = 0; // hash value for pattern  
+    int t = 0; // hash value for txt  
+    int h = 1;  
+
+    // The value of h would be "pow(d, M-1)%q"  
+    for (i = 0; i < M - 1; i++)  
+        h = (h * d) % q;  
+
+    // Calculate the hash value of pattern and first  
+    // window of text  
+    for (i = 0; i < M; i++)  
+    {  
+        p = (d * p + pat[i]) % q;  
+        t = (d * t + txt[i]) % q;  
+    }  
+
+    // Slide the pattern over text one by one  
+    for (i = 0; i <= N - M; i++)  
+    {  
+
+        // Check the hash values of current window of text  
+        // and pattern. If the hash values match then only  
+        // check for characters on by one  
+        if ( p == t )  
+        {  
+            /* Check for characters one by one */
+            for (j = 0; j < M; j++)  
+            {  
+                if (txt[i+j] != pat[j])  
+                    break;  
+            }  
+
+            // if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]  
+            if (j == M)  
+                cout<<"Pattern found at index "<< i<<endl;  
+        }  
+
+        // Calculate hash value for next window of text: Remove  
+        // leading digit, add trailing digit  
+        if ( i < N-M )  
+        {  
+            t = (d*(t - txt[i]*h) + txt[i+M])%q;  
+
+            // We might get negative value of t, converting it  
+            // to positive  
+            if (t < 0)  
+            t = (t + q);  
+        }  
+    }  
+}  
+
+/* Driver code */
+int main()  
+{  
+    char txt[] = "GEEKS FOR GEEKS";  
+    char pat[] = "GEEK"; 
+
+      // A prime number  
+    int q = 101;  
+
+      // Function Call 
+      search(pat, txt, q);  
+    return 0;  
+}