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72 lines
2.2 KiB
Java
72 lines
2.2 KiB
Java
import java.math.BigInteger;
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import java.util.Random;
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public class Hashing {
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static final int multiplier = 43;
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static final Random rnd = new Random();
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static final int mod1 = BigInteger.valueOf((int) (1e9 + rnd.nextInt((int) 1e9))).nextProbablePrime().intValue();
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static final int mod2 = BigInteger.valueOf((int) (1e9 + rnd.nextInt((int) 1e9))).nextProbablePrime().intValue();
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static final int invMultiplier1 = BigInteger.valueOf(multiplier).modInverse(BigInteger.valueOf(mod1)).intValue();
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static final int invMultiplier2 = BigInteger.valueOf(multiplier).modInverse(BigInteger.valueOf(mod2)).intValue();
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long[] hash1, hash2;
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long[] inv1, inv2;
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int n;
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public Hashing(String s) {
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n = s.length();
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hash1 = new long[n + 1];
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hash2 = new long[n + 1];
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inv1 = new long[n + 1];
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inv2 = new long[n + 1];
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inv1[0] = 1;
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inv2[0] = 1;
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long p1 = 1;
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long p2 = 1;
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for (int i = 0; i < n; i++) {
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hash1[i + 1] = (hash1[i] + s.charAt(i) * p1) % mod1;
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p1 = p1 * multiplier % mod1;
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inv1[i + 1] = inv1[i] * invMultiplier1 % mod1;
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hash2[i + 1] = (hash2[i] + s.charAt(i) * p2) % mod2;
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p2 = p2 * multiplier % mod2;
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inv2[i + 1] = inv2[i] * invMultiplier2 % mod2;
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}
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}
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public long getHash(int i, int len) {
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return (((hash1[i + len] - hash1[i] + mod1) * inv1[i] % mod1) << 32)
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+ (hash2[i + len] - hash2[i] + mod2) * inv2[i] % mod2;
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}
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// random test
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public static void main(String[] args) {
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Random rnd = new Random(1);
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for (int step = 0; step < 1000; step++) {
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int n1 = rnd.nextInt(50);
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String s1 = getRandomString(n1, rnd);
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int n2 = rnd.nextInt(50);
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String s2 = getRandomString(n2, rnd);
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Hashing h1 = new Hashing(s1);
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Hashing h2 = new Hashing(s2);
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for (int k = 0; k < 1000; k++) {
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int i1 = rnd.nextInt(n1 + 1);
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int j1 = rnd.nextInt(n1 - i1 + 1) + i1;
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int i2 = rnd.nextInt(n2 + 1);
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int j2 = rnd.nextInt(n2 - i2 + 1) + i2;
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if (s1.substring(i1, j1).equals(s2.substring(i2, j2)) != (h1.getHash(i1, j1 - i1) == h2.getHash(i2, j2 - i2)))
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throw new RuntimeException();
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}
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}
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}
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static String getRandomString(int n, Random rnd) {
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char[] s = new char[n];
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for (int i = 0; i < n; i++) {
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s[i] = (char) ('a' + rnd.nextInt(3));
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}
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return new String(s);
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}
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}
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