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Rabin-Karp Algorithm for string matching

md soyeb answered on July 26, 2022 Popularity 7/10 Helpfulness 4/10

answer Rabin-Karp Algorithm for string matching

related Rabin-Karp String Searching Algorithm

Rabin-Karp Algorithm for string matching

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vector<int> rabin_karp(string const& s, string const& t) {
    const int p = 31; 
    const int m = 1e9 + 9;
    int S = s.size(), T = t.size();

    vector<long long> p_pow(max(S, T)); 
    p_pow[0] = 1; 
    for (int i = 1; i < (int)p_pow.size(); i++) 
        p_pow[i] = (p_pow[i-1] * p) % m;

    vector<long long> h(T + 1, 0); 
    for (int i = 0; i < T; i++)
        h[i+1] = (h[i] + (t[i] - 'a' + 1) * p_pow[i]) % m; 
    long long h_s = 0; 
    for (int i = 0; i < S; i++) 
        h_s = (h_s + (s[i] - 'a' + 1) * p_pow[i]) % m; 

    vector<int> occurences;
    for (int i = 0; i + S - 1 < T; i++) { 
        long long cur_h = (h[i+S] + m - h[i]) % m; 
        if (cur_h == h_s * p_pow[i] % m)
            occurences.push_back(i);
    }
    return occurences;
}

Popularity 7/10 Helpfulness 4/10 Language cpp

Source: cp-algorithms.com

Tags: algorithm c++ rabin-karp string-matching

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Contributed on Nov 18 2022

md soyeb

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Rabin-Karp String Searching Algorithm

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Compares hash values of substrings to save time
only double check if really a match when the hash values match (else there is no point). 
Versus brute force(compare every letter), far fewer comparisons

Popularity 7/10 Helpfulness 1/10 Language whatever

Source: Grepper

Tags: whatever rabin-karp algorithm alg

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Contributed on Jul 26 2022

Javasper

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Rabin-Karp Algorithm for string matching

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Rabin-Karp Algorithm for string matching

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