Rust字符串匹配Rabin-Karp算法详解

fn rabin_karp(text: &str, pattern: &str) -> Vec<usize> {
    let n = text.len();
    let m = pattern.len();
    let base: u64 = 256;
    let modulus: u64 = 101;
    let mut res = Vec::new();

    if m > n {
        return res;
    }

    // Precompute (base ** (m - 1)) % modulus
    let mut h: u64 = 1;
    for _ in 0..m - 1 {
        h = (h * base) % modulus;
    }

    // Compute the hash value of pattern and first window of text
    let mut p: u64 = 0;
    let mut t: u64 = 0;
    for i in 0..m {
        p = (base * p + pattern.as_bytes()[i] as u64) % modulus;
        t = (base * t + text.as_bytes()[i] as u64) % modulus;
    }

    // Slide the pattern over text one by one
    for i in 0..n - m + 1 {
        // Check the hash values of current window of text and pattern
        if p == t {
            // Check if the characters are actually the same
            if text[i..i + m] == *pattern {
                res.push(i);
            }
        }

        // Calculate the hash value for next window of text
        if i < n - m {
            t = (base * (t - text.as_bytes()[i] as u64 * h) + text.as_bytes()[i + m] as u64) % modulus;

            // We might get negative value of t, converting it to positive
            if t < 0 {
                t += modulus;
            }
        }
    }

    res
}