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class Encoder:
def __init__(self, string, to_show, warning: int = None, mod_value=11):
self.control = warning if warning is not None else to_show
self.range = [0, to_show]
self.hashed = 0
self.container = []
"""to avoid large value not needed in python (but consumes large space if ignored)"""
self.mod_value = mod_value
self.encode_them(string)
def encode_them(self, string):
self.container = [ord(_) for _ in string]
length = self.range[1] - self.range[0]
for i in range(length):
self.hashed += self.container[i] * (10 ** ((length - i - 1) % self.mod_value))
def shift(self):
if self.range[1] >= self.control:
return ""
length = self.range[1] - self.range[0]
self.hashed -= self.container[self.range[0]] * (10 ** ((length - 1) % self.mod_value))
self.hashed *= 10
self.hashed += self.container[self.range[1]]
self.range[0], self.range[1] = self.range[0] + 1, self.range[1] + 1
def rabin_karp_match(main_string, sub_string, mod_value=11):
main_length, sub_length = len(main_string), len(sub_string)
if sub_string == 0:
return 0
if sub_length > main_length:return -1
main, sub = Encoder(main_string, sub_length, main_length, mod_value), Encoder(sub_string, sub_length, warning=None,
mod_value=mod_value)
matches = [0]
for i in range(main_length - sub_length + 1):
if main.hashed == sub.hashed:
if main_string[i: i + sub_length] == sub_string:
matches[0] += 1
matches.append(i)
main.shift()
return tuple(matches)
print(rabin_karp_match("Rem-Rem", "Rem", 2))
print(rabin_karp_match("AYA-AYA", "AYA"))
print(rabin_karp_match("JOJO", "JO"))
print(rabin_karp_match("aaaa", "b"))
print(rabin_karp_match("sd",""))
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// Rabin Karp Alogorithm - (search substring)
#include <iostream>
#include <string>
using namespace std;
#define ll long long
#define BASE 227
#define MOD 1000000007
ll hhash(string s, ll l = -1) {
if (l == -1)
l = s.size();
ll h = 0;
for (ll i = 0; i < l; i++)
h = (h * BASE + s[i]) % MOD;
return h;
}
ll rabin_karp(string s, string t) {
ll h1 = hhash(t), h2 = hhash(s, t.size());
if (h1 == h2)
return 0;
ll power = 1;
for (ll i = 0; i < t.size(); i++)
power = (power * BASE) % MOD;
for (ll i = t.size(); i < s.size(); i++) {
h2 = (h2*BASE + s[i]) % MOD;
h2 = (h2 - (power * s[i-t.size()] % MOD) + MOD) % MOD;
if (h1 == h2)
return i - (t.size() - 1);
}
return -1;
}
int main() {
string s, t;
cin>>s>>t;
ll ans = rabin_karp(s, t);
if(ans == -1)
cout<<"String not found"<<endl;
else
cout<<"String \""<<t<<"\" found at position "<<ans<<endl;
return 0;
}
//Time Complexity: O(n)
//Space Complexity: O(n)
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1 function RabinKarp(string s[1..n], string pattern[1..m])
2 hpattern := hash(pattern[1..m]);
3 for i from 1 to n-m+1
4 hs := hash(s[i..i+m-1])
5 if hs = hpattern
6 if s[i..i+m-1] = pattern[1..m]
7 return i
8 return not found
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//C++ code for implementation of Rabin Karp algorithm
#include <bits/stdc++.h>
using namespace std;
// Function for searching a pattern in a string using Rabin Karp algorithm
void rabinKarpSearch(string S, string P)
{
// Calculating the length of S and P
int Ns = S.length();
int Np = P.length();
// Initialize the value of prime number and mod for calculating hash values
int prime = 31;
int mod = 1e9 + 9;
// Calculating the power raise to the taken prime
vector<long long> p_pow(Ns);
p_pow[0] = 1;
for (int i = 1; i < Ns; i++)
{
p_pow[i] = (p_pow[i-1] * prime) % mod;
}
vector<long long> h(Ns + 1, 0);
for (int i = 0; i < Ns; i++)
{
h[i+1] = (h[i] + (S[i] - 'a' + 1) * p_pow[i]) % mod;
}
// Calculating the hash value of P
long long hash_P = 0;
for (int i = 0; i < Np; i++)
{
hash_P = (hash_P + (P[i] - 'a' + 1) * p_pow[i]) % mod;
}
/*
Now slide the pattern by one character and check for the corresponding
hash value to match with the hash value of the given pattern
*/
for (int i = 0; i + Np - 1 < Ns; i++)
{
long long curr_hash = (h[i+Np] + mod - h[i]) % mod;
if (curr_hash == hash_P * p_pow[i] % mod)
cout<<"The given pattern occurs in the given string at index "<<i<<endl;
}
}
int main()
{
string S = "cxyzghxyzvjkxyz";
string P = "xyz";
// Call the function for rabin karp algorithm
rabinKarpSearch(S,P);
return 0;
}