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Commit 85a2df4

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To add Suffix array algorithm implementation (#6530)
* adding Suffix Array Implementation * adding test for Suffix Array * patch: lint fix in SuffixArray.java * patch: lint fix in SuffixArrayTest.java * fix: private constructor update * patch: lint fix in suffix array impl * fix: lint issue line blankspace removal * fix: checkstype issue * fix: lint format issue * Update DIRECTORY.md
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‎DIRECTORY.md‎

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- 📄 [Rotation](src/main/java/com/thealgorithms/strings/Rotation.java)
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- 📄 [StringCompression](src/main/java/com/thealgorithms/strings/StringCompression.java)
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- 📄 [StringMatchFiniteAutomata](src/main/java/com/thealgorithms/strings/StringMatchFiniteAutomata.java)
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- 📄 [SuffixArray](src/main/java/com/thealgorithms/strings/SuffixArray.java)
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- 📄 [Upper](src/main/java/com/thealgorithms/strings/Upper.java)
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- 📄 [ValidParentheses](src/main/java/com/thealgorithms/strings/ValidParentheses.java)
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- 📄 [WordLadder](src/main/java/com/thealgorithms/strings/WordLadder.java)
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- 📄 [RotationTest](src/test/java/com/thealgorithms/strings/RotationTest.java)
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- 📄 [StringCompressionTest](src/test/java/com/thealgorithms/strings/StringCompressionTest.java)
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- 📄 [StringMatchFiniteAutomataTest](src/test/java/com/thealgorithms/strings/StringMatchFiniteAutomataTest.java)
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- 📄 [SuffixArrayTest](src/test/java/com/thealgorithms/strings/SuffixArrayTest.java)
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- 📄 [UpperTest](src/test/java/com/thealgorithms/strings/UpperTest.java)
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- 📄 [ValidParenthesesTest](src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java)
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- 📄 [WordLadderTest](src/test/java/com/thealgorithms/strings/WordLadderTest.java)
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package com.thealgorithms.strings;
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import java.util.Arrays;
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/**
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* Suffix Array implementation in Java.
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* Builds an array of indices that represent all suffixes of a string in sorted order.
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* Wikipedia Reference: https://en.wikipedia.org/wiki/Suffix_array
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* Author: Nithin U.
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* Github: https://github.com/NithinU2802
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*/
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public final class SuffixArray {
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private SuffixArray() {
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}
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public static int[] buildSuffixArray(String text) {
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int n = text.length();
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Integer[] suffixArray = new Integer[n];
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int[] rank = new int[n];
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int[] tempRank = new int[n];
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// Initial ranking based on characters
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for (int i = 0; i < n; i++) {
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suffixArray[i] = i;
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rank[i] = text.charAt(i);
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}
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for (int k = 1; k < n; k *= 2) {
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final int step = k;
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// Comparator: first by rank, then by rank + step
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Arrays.sort(suffixArray, (a, b) -> {
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if (rank[a] != rank[b]) {
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return Integer.compare(rank[a], rank[b]);
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}
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int ra = (a + step < n) ? rank[a + step] : -1;
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int rb = (b + step < n) ? rank[b + step] : -1;
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return Integer.compare(ra, rb);
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});
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// Re-rank
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tempRank[suffixArray[0]] = 0;
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for (int i = 1; i < n; i++) {
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int prev = suffixArray[i - 1];
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int curr = suffixArray[i];
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boolean sameRank = rank[prev] == rank[curr] && ((prev + step < n ? rank[prev + step] : -1) == (curr + step < n ? rank[curr + step] : -1));
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tempRank[curr] = sameRank ? tempRank[prev] : tempRank[prev] + 1;
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}
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System.arraycopy(tempRank, 0, rank, 0, n);
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if (rank[suffixArray[n - 1]] == n - 1) {
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break;
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}
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}
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return Arrays.stream(suffixArray).mapToInt(Integer::intValue).toArray();
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}
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}
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package com.thealgorithms.strings;
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import static org.junit.jupiter.api.Assertions.assertArrayEquals;
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import org.junit.jupiter.api.Test;
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class SuffixArrayTest {
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@Test
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void testEmptyString() {
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int[] result = SuffixArray.buildSuffixArray("");
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assertArrayEquals(new int[] {}, result, "Empty string should return empty suffix array");
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}
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@Test
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void testSingleCharacter() {
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int[] result = SuffixArray.buildSuffixArray("a");
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assertArrayEquals(new int[] {0}, result, "Single char string should return [0]");
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}
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@Test
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void testDistinctCharacters() {
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int[] result = SuffixArray.buildSuffixArray("abc");
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assertArrayEquals(new int[] {0, 1, 2}, result, "Suffixes already in order for distinct chars");
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}
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@Test
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void testBananaExample() {
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int[] result = SuffixArray.buildSuffixArray("banana");
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assertArrayEquals(new int[] {5, 3, 1, 0, 4, 2}, result, "Suffix array of 'banana' should be [5,3,1,0,4,2]");
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}
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@Test
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void testStringWithDuplicates() {
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int[] result = SuffixArray.buildSuffixArray("aaaa");
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assertArrayEquals(new int[] {3, 2, 1, 0}, result, "Suffix array should be descending indices for 'aaaa'");
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}
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@Test
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void testRandomString() {
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int[] result = SuffixArray.buildSuffixArray("mississippi");
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assertArrayEquals(new int[] {10, 7, 4, 1, 0, 9, 8, 6, 3, 5, 2}, result, "Suffix array for 'mississippi' should match expected");
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}
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}

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