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18.RabinKarp.cpp

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+/*
+ * This program searches for a pattern in a text using
+ * Rabin - Karp Algorithm
+ *
+ *      Coded by: Abdurrezak Efe
+ *
+ * */
+
+
+
+#include <iostream>
+#include <cmath>
+#include <vector>
+using namespace std;
+
+int prime = 7;
+int pattern_hash;
+vector<int> indexes;
+
+int hasher(string s)
+{
+    int result = 0;
+    for(int i=0;i<s.size();i++)
+        result += (s[i] - 'a' + 1)*pow(prime, s.size()-i-1);
+
+    return result;
+}
+
+void rabin_karp(string text, string pattern)
+{
+    int m = pattern.size();
+
+    int cur_hash = hasher(text.substr(0,m));
+
+    //cout << cur_hash << endl;
+
+    for(int i=0; i < text.size()-m+1; i++) //searching
+    {
+        if(cur_hash == pattern_hash)
+            if(text.substr(i,m) == pattern)
+                indexes.push_back(i);
+
+        cur_hash = prime*(cur_hash - (text[i]-'a'+1)*pow(prime, m-1))+(text[i+m]-'a'+1); //updating hash in O(1)
+    }
+}
+
+
+int main()
+{
+    string text, pattern;
+    cin >> text >> pattern;
+
+    pattern_hash = hasher(pattern);
+    rabin_karp(text, pattern);
+
+    for(int i=0;i<indexes.size();i++)
+        cout << indexes[i] << endl;
+
+}