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feat(compression): Add LZ77 and LZ78 algorithms (#6910)
* feat(compression): Add LZ77 and LZ78 algorithms * Resolve Spotbugs warning in LZ78 by using Trie structure * fix code style
This commit is contained in:
Indole Yi
295
src/test/java/com/thealgorithms/compression/LZ78Test.java
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295
src/test/java/com/thealgorithms/compression/LZ78Test.java
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package com.thealgorithms.compression;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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import java.util.List;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.Test;
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class LZ78Test {
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@Test
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@DisplayName("Test compression and decompression of a simple repeating string")
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void testSimpleRepeatingString() {
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String original = "ababcbababaa";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test compression and decompression example ABAABABAABAB")
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void testStandardExample() {
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String original = "ABAABABAABAB";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Verify the compression produces expected tokens
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// Expected: (0,A)(0,B)(1,A)(2,B)(3,A)(4,B)
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// Where dictionary builds as: 1:A, 2:B, 3:AA, 4:BA, 5:ABA, 6:BAB
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assertEquals(6, compressed.size());
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assertEquals(0, compressed.get(0).index());
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assertEquals('A', compressed.get(0).nextChar());
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assertEquals(0, compressed.get(1).index());
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assertEquals('B', compressed.get(1).nextChar());
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assertEquals(1, compressed.get(2).index());
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assertEquals('A', compressed.get(2).nextChar());
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}
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@Test
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@DisplayName("Test compression and decompression of a longer example")
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void testLongerExample() {
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String original = "TOBEORNOTTOBEORTOBEORNOT";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test empty string compression and decompression")
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void testEmptyString() {
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String original = "";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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assertTrue(compressed.isEmpty());
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}
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@Test
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@DisplayName("Test null string compression")
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void testNullStringCompress() {
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List<LZ78.Token> compressed = LZ78.compress(null);
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assertTrue(compressed.isEmpty());
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}
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@Test
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@DisplayName("Test null list decompression")
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void testNullListDecompress() {
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String decompressed = LZ78.decompress(null);
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assertEquals("", decompressed);
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}
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@Test
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@DisplayName("Test string with all same characters")
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void testAllSameCharacters() {
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String original = "AAAAAA";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Should achieve good compression: (0,A)(1,A)(2,A)...
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assertTrue(compressed.size() <= 4); // Builds: A, AA, AAA, etc.
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}
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@Test
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@DisplayName("Test string with all unique characters")
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void testAllUniqueCharacters() {
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String original = "abcdefg";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// No compression for unique characters
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assertEquals(original.length(), compressed.size());
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// Each token should have index 0 (empty prefix)
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for (LZ78.Token token : compressed) {
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assertEquals(0, token.index());
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}
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}
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@Test
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@DisplayName("Test single character string")
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void testSingleCharacter() {
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String original = "a";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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assertEquals(1, compressed.size());
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assertEquals(0, compressed.getFirst().index());
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assertEquals('a', compressed.getFirst().nextChar());
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}
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@Test
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@DisplayName("Test two character string")
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void testTwoCharacters() {
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String original = "ab";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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assertEquals(2, compressed.size());
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}
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@Test
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@DisplayName("Test repeating pairs")
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void testRepeatingPairs() {
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String original = "ababab";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Should compress well: (0,a)(0,b)(1,b) or similar
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assertTrue(compressed.size() < original.length());
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}
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@Test
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@DisplayName("Test growing patterns")
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void testGrowingPatterns() {
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String original = "abcabcdabcde";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test dictionary building correctness")
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void testDictionaryBuilding() {
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String original = "aabaabaab";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Verify first few tokens
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// Expected pattern: (0,a)(1,b)(2,a)(3,b) building dictionary 1:a, 2:ab, 3:aa, 4:aab
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assertTrue(compressed.size() > 0);
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assertEquals(0, compressed.getFirst().index()); // First char always has index 0
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}
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@Test
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@DisplayName("Test with special characters")
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void testSpecialCharacters() {
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String original = "hello world! hello!";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test with numbers")
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void testWithNumbers() {
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String original = "1234512345";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Should achieve compression
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assertTrue(compressed.size() < original.length());
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}
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@Test
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@DisplayName("Test long repeating sequence")
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void testLongRepeatingSequence() {
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String original = "abcdefgh".repeat(5);
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// LZ78 should achieve some compression for repeating sequences
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assertTrue(compressed.size() < original.length(), "Compressed size should be less than original length");
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}
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@Test
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@DisplayName("Test alternating characters")
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void testAlternatingCharacters() {
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String original = "ababababab";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test compression effectiveness")
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void testCompressionEffectiveness() {
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String original = "the quick brown fox jumps over the lazy dog the quick brown fox";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Should achieve some compression due to repeated phrases
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assertTrue(compressed.size() < original.length());
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}
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@Test
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@DisplayName("Test with mixed case letters")
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void testMixedCase() {
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String original = "AaBbCcAaBbCc";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test palindrome string")
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void testPalindrome() {
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String original = "abccba";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test highly compressible pattern")
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void testHighlyCompressible() {
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String original = "aaaaaaaaaa";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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// Should achieve excellent compression ratio
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assertTrue(compressed.size() <= 4);
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}
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@Test
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@DisplayName("Test empty list decompression")
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void testEmptyListDecompress() {
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List<LZ78.Token> compressed = List.of();
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String decompressed = LZ78.decompress(compressed);
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assertEquals("", decompressed);
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}
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@Test
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@DisplayName("Test binary-like pattern")
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void testBinaryPattern() {
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String original = "0101010101";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test nested patterns")
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void testNestedPatterns() {
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String original = "abcabcdefabcdefghi";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test whitespace handling")
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void testWhitespace() {
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String original = "a b c a b c";
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List<LZ78.Token> compressed = LZ78.compress(original);
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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@Test
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@DisplayName("Test token structure correctness")
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void testTokenStructure() {
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String original = "abc";
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List<LZ78.Token> compressed = LZ78.compress(original);
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// All tokens should have valid indices (>= 0)
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for (LZ78.Token token : compressed) {
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assertTrue(token.index() >= 0);
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assertNotNull(token.nextChar());
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}
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String decompressed = LZ78.decompress(compressed);
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assertEquals(original, decompressed);
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}
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}
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