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40 lines
1.3 KiB
Java
40 lines
1.3 KiB
Java
import java.util.*;
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import java.util.stream.IntStream;
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// https://en.wikipedia.org/wiki/Suffix_array
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public class SuffixArray2 {
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// suffix array in O(n*log^2(n))
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public static int[] suffixArray(CharSequence s) {
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int n = s.length();
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Integer[] sa = IntStream.range(0, n).mapToObj(Integer::valueOf).toArray(Integer[]::new);
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int[] rank = s.chars().toArray();
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for (int len = 1; len < n; len *= 2) {
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long[] rank2 = new long[n];
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for (int i = 0; i < n; i++)
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rank2[i] = ((long) rank[i] << 32) + (i + len < n ? rank[i + len] + 1 : 0);
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Arrays.sort(sa, (a, b) -> Long.compare(rank2[a], rank2[b]));
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for (int i = 0; i < n; i++)
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rank[sa[i]] = i > 0 && rank2[sa[i - 1]] == rank2[sa[i]] ? rank[sa[i - 1]] : i;
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}
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return Arrays.stream(sa).mapToInt(Integer::intValue).toArray();
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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 < 100000; step++) {
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int n = rnd.nextInt(100);
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StringBuilder s = rnd.ints(n, 0, 10).collect(StringBuilder::new, (sb, i) -> sb.append((char) ('\1' + i)), StringBuilder::append);
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int[] sa = suffixArray(s);
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for (int i = 0; i + 1 < n; i++)
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if (s.substring(sa[i]).compareTo(s.substring(sa[i + 1])) >= 0)
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throw new RuntimeException();
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}
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System.out.println("Test passed");
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}
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}
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