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SuffixArray.java
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SuffixArray.java
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package com.algorithm.playground.data.structure;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.function.IntBinaryOperator;
public class SuffixArray {
private int[] array;
private String string;
public SuffixArray(String string) {
this.string = string;
this.array = SuffixArrayUtils.buildSuffixArrayNaive(string);
}
public int getFirst(String s) {
int idx = getIdx(s);
return idx == -1 ? -1 : reduce(s, array[idx], idx, Math::min);
}
public int getLast(String s) {
int idx = getIdx(s);
return idx == -1 ? -1 : reduce(s, array[idx], idx, Math::max);
}
public int count(String s) {
int idx = getIdx(s);
return idx == -1 ? 0 : reduce(s, 1, idx, (count, ignored) -> count + 1);
}
public boolean contains(String s) {
return getIdx(s) != -1;
}
@Override
public String toString() {
int len = countDigits(array.length);
StringBuilder builder = new StringBuilder();
for (int i : array) {
builder.append("\t\t")
.append(padding(i, len))
.append(" : <")
.append(string.substring(i))
.append(">\n");
}
return "SuffixArray{\n" + builder + '}';
}
private int reduce(String s, int value, int idx, IntBinaryOperator op) {
for (int l = idx - 1; l >= 0 && compareSubstrings(s, array[l]) == 0; l--) {
value = op.applyAsInt(value, array[l]);
}
for (int r = idx + 1; r < array.length && compareSubstrings(s, array[r]) == 0; r++) {
value = op.applyAsInt(value, array[r]);
}
return value;
}
private int getIdx(String s) {
int lo = 0, hi = array.length - 1;
while (lo <= hi) {
int mid = (hi - lo >> 1) + lo;
int compare = compareSubstrings(s, array[mid]);
if (compare < 0) {
lo = mid + 1;
} else if (compare > 0) {
hi = mid - 1;
} else {
return mid;
}
}
return -1;
}
private int compareSubstrings(String pattern, int idx) {
int i = 0;
for (; i < pattern.length() && idx < string.length(); i++, idx++) {
char ch1 = string.charAt(idx);
char ch2 = pattern.charAt(i);
if (ch1 != ch2) {
return ch1 - ch2;
}
}
return i == pattern.length() ? 0 : -1;
}
private String padding(int i, int len) {
len = len - countDigits(i);
StringBuilder builder = new StringBuilder();
for (int j = 0; j < len; j++) {
builder.append(' ');
}
return builder.append(i).toString();
}
private int countDigits(int i) {
int count = i == 0 ? 1 : 0;
//noinspection StatementWithEmptyBody
for (; i > 0; count++, i /= 10) ;
return count;
}
private static class SuffixArrayUtils {
/**
* The simplest way to constract a suffix array, just to sort all substrings
*
* @param string
*
* @return
*/
private static int[] buildSuffixArrayNaive(String string) {
int[] array = new int[string.length()];
List<Integer> indexes = new ArrayList<>(string.length());
for (int i = 0; i < array.length; i++) {
indexes.add(i);
}
indexes.sort((i1, i2) -> compare(i1, i2, string));
for (int i = 0; i < array.length; i++) {
array[i] = indexes.get(i);
}
return array;
}
/**
* Performs sorting by rank in order to build a suffix array
*
* @param string
*
* @return
*/
private static int[] buildSuffixArrayRankSort(String string) {
int[] array = new int[string.length()];
Suffix[] suffixes = new Suffix[string.length()];
int N = string.length();
for (int i = 0; i < N; i++) {
Suffix suffix = new Suffix();
suffix.idx = i;
suffix.rank = string.charAt(i);
suffix.nextRank = i + 1 < N ? string.charAt(i + 1) : -1;
suffixes[i] = suffix;
}
Arrays.sort(suffixes);
for (int k = 4; k < N << 1; k <<= 1) {
int rank = 0;
int prev = suffixes[0].rank;
suffixes[0].rank = rank;
array[suffixes[0].idx] = rank;
for (int i = 1; i < N; i++) {
if (suffixes[i].rank == prev && suffixes[i].nextRank == suffixes[i - 1].nextRank) {
prev = suffixes[i].rank;
suffixes[i].rank = rank;
} else {
prev = suffixes[i].rank;
suffixes[i].rank = ++rank;
}
array[suffixes[i].idx] = i;
}
for (int i = 0; i < N; i++) {
int next = suffixes[i].idx + (k >> 1);
suffixes[i].nextRank = next < N ? suffixes[array[next]].rank : -1;
}
Arrays.sort(suffixes);
}
for (int i = 0; i < N; i++) {
array[i] = suffixes[i].idx;
}
return array;
}
/**
* Sort substrings by one character
*
* @param string
*
* @return
*/
private static int[] buildSuffixArrayRadixSort(String string) {
int[] array = new int[string.length()];
int[][] suffixes = new int[string.length()][2];
int N = string.length();
for (int i = 0; i < N; i++) {
suffixes[i][0] = i;
}
Arrays.sort(suffixes, charComparator(0, string));
for (int i = 0; i < N - 1; i++) {
array[0] = suffixes[0][0];
int rank = 0, prevRank = 0, len = 1;
for (int j = 1; j < suffixes.length; j++) {
array[j] = suffixes[j][0];
int[] prev = suffixes[j - 1];
int[] curr = suffixes[j];
if (curr[0] + i < N && prev[0] + i < N && curr[1] == prevRank) {
char ch1 = string.charAt(curr[0] + i);
char ch2 = string.charAt(prev[0] + i);
prevRank = curr[1];
if (ch1 == ch2) {
len++;
curr[1] = rank;
} else {
if (len > 1) {
Arrays.sort(suffixes, j - len, j, charComparator(i + 1, string));
}
len = 1;
curr[1] = ++rank;
}
} else {
if (len > 1) {
Arrays.sort(suffixes, j - len, j, charComparator(i + 1, string));
}
len = 1;
prevRank = curr[1];
curr[1] = ++rank;
}
}
if (len > 1) {
Arrays.sort(suffixes, suffixes.length - len, suffixes.length, charComparator(i + 1, string));
} else if (rank + 1 == N) {
break;
}
}
return array;
}
private static Comparator<int[]> charComparator(int idx, String string) {
return (s1, s2) -> {
if (s1[1] != s2[1]) {
return s1[1] - s2[1];
}
if (s1[0] + idx >= string.length() || s2[0] + idx >= string.length()) {
return s2[0] - s1[0];
}
char ch1 = string.charAt(s1[0] + idx);
char ch2 = string.charAt(s2[0] + idx);
return ch1 - ch2;
};
}
private static int compare(int i1, int i2, String string) {
while (i1 < string.length() && i2 < string.length()) {
char ch1 = string.charAt(i1++);
char ch2 = string.charAt(i2++);
if (ch1 != ch2) {
return ch1 - ch2;
}
}
return i2 - i1;
}
private static class Suffix implements Comparable<Suffix> {
private int idx;
private int rank;
private int nextRank;
@Override
public int compareTo(Suffix that) {
if (rank == that.rank) {
return nextRank - that.nextRank;
} else {
return rank - that.rank;
}
}
@Override
public String toString() {
return "Suffix{" +
"idx=" + idx +
", rank=" + rank +
", nextRank=" + nextRank +
'}';
}
}
}
}