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50 lines
1.2 KiB
Java
50 lines
1.2 KiB
Java
import java.util.Random;
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public class ZFunction {
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// z[i] = lcp(s[0..], s[i..])
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public static int[] zFunction(String s) {
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int[] z = new int[s.length()];
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for (int i = 1, l = 0, r = 0; i < z.length; ++i) {
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if (i <= r)
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z[i] = Math.min(r - i + 1, z[i - l]);
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while (i + z[i] < z.length && s.charAt(z[i]) == s.charAt(i + z[i]))
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++z[i];
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if (r < i + z[i] - 1) {
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l = i;
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r = i + z[i] - 1;
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}
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}
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return z;
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}
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// random tests
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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 < 10_000; step++) {
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String s = getRandomString(rnd, 100);
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String pattern = getRandomString(rnd, 5);
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int pos1 = find(s, pattern);
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int pos2 = s.indexOf(pattern);
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if (pos1 != pos2)
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throw new RuntimeException();
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}
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}
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static int find(String s, String pattern) {
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int[] z = zFunction(pattern + "\0" + s);
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for (int i = pattern.length() + 1; i < z.length; i++)
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if (z[i] == pattern.length())
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return i - pattern.length() - 1;
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return -1;
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}
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static String getRandomString(Random rnd, int maxlen) {
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int n = rnd.nextInt(maxlen) + 1;
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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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return new String(s);
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}
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}
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