查找给定哈希值的子串

/*
 * Solution Approach:
 * 1. Utilize Java Streams to find the substring with the given hashValue.
 * 2. Convert characters to values and use IntStream to calculate the hash.
 * 3. Find the first matching hash using the Streams API.
 */
import java.util.stream.IntStream;

public class SolutionStream {
    public String subStringWithGivenHash(String s, int power, int modulo, int k, int hashValue) {
        return IntStream.rangeClosed(0, s.length() - k)
                .filter(i -> hash(s.substring(i, i + k), power, modulo) == hashValue)
                .mapToObj(i -> s.substring(i, i + k))
                .findFirst()
                .orElse("");
    }

    private int hash(String sub, int power, int modulo) {
        int hash = 0;
        long powerFactor = 1;
        for (int i = 0; i < sub.length(); i++) {
            hash = (int) ((hash + (sub.charAt(i) - 'a' + 1) * powerFactor) % modulo);
            powerFactor = (powerFactor * power) % modulo;
        }
        return hash;
    }
}