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feat: Add KMP Substring Search Algorithm (#231)
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‎README.md

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}
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```
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### KMP Substring Search Algorithm
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```java
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public class KMPSubstringSearchSnippet {
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/**
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* Implements the Knuth-Morris-Pratt (KMP) algorithm to find the index of the first occurrence of a substring in a given text.
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*
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* @param text The text in which the substring is to be searched.
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* @param pattern The substring pattern to search for.
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* @return The index of the first occurrence of the pattern in the text, or -1 if the pattern is not found.
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*/
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public static int kmpSearch(String text, String pattern) {
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if (pattern == null || pattern.length() == 0) {
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return 0; // Trivial case: empty pattern
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}
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int[] lps = computeLPSArray(pattern);
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int i = 0; // index for text
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int j = 0; // index for pattern
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while (i < text.length()) {
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if (pattern.charAt(j) == text.charAt(i)) {
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i++;
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j++;
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}
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if (j == pattern.length()) {
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return i - j; // Found pattern at index (i - j)
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} else if (i < text.length() && pattern.charAt(j) != text.charAt(i)) {
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if (j != 0) {
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j = lps[j - 1]; // Use the LPS array to skip characters
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} else {
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i++; // If no match and j is 0, move to the next character in text
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}
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}
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}
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return -1; // Pattern not found
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}
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/**
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* Computes the LPS (Longest Prefix Suffix) array for the pattern, which indicates the longest proper prefix which is also a suffix.
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*
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* @param pattern The pattern for which the LPS array is to be computed.
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* @return The LPS array.
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*/
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private static int[] computeLPSArray(String pattern) {
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int length = 0;
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int i = 1;
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int[] lps = new int[pattern.length()];
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lps[0] = 0; // LPS for the first character is always 0
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while (i < pattern.length()) {
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if (pattern.charAt(i) == pattern.charAt(length)) {
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length++;
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lps[i] = length;
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i++;
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} else {
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if (length != 0) {
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length = lps[length - 1]; // Fall back to the previous LPS value
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} else {
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lps[i] = 0;
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i++;
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}
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}
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}
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return lps;
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}
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}
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```
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## Thread
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### Thread Pool

‎src/main/java/string/KmpSubstringSearchSnippet.java

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/*
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* MIT License
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*
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* Copyright (c) 2017-2024 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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package string;
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/**
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* KmpSubstringSearchSnippet.
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*/
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public class KmpSubstringSearchSnippet {
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/**
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* Implements the Knuth-Morris-Pratt (KMP) algorithm to find the of a substring.
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*
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* @param text The text in which the substring is to be searched.
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* @param pattern The substring pattern to search for.
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* @return The index of the first occurrence, or -1 if the pattern is not found.
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*/
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public static int kmpSearch(String text, String pattern) {
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if (pattern == null || pattern.length() == 0) {
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return 0; // Trivial case: empty pattern
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}
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int[] lps = computeLpsArray(pattern);
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int i = 0; // index for text
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int j = 0; // index for pattern
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while (i < text.length()) {
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if (pattern.charAt(j) == text.charAt(i)) {
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i++;
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j++;
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}
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if (j == pattern.length()) {
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return i - j; // Found pattern at index (i - j)
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} else if (i < text.length() && pattern.charAt(j) != text.charAt(i)) {
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if (j != 0) {
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j = lps[j - 1]; // Use the LPS array to skip characters
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} else {
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i++; // If no match and j is 0, move to the next character in text
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}
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}
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}
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return -1; // Pattern not found
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}
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/**
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* Computes the LPS (Longest Prefix Suffix) array, which indicates the longest proper prefix.
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*
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* @param pattern The pattern for which the LPS array is to be computed.
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* @return The LPS array.
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*/
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private static int[] computeLpsArray(String pattern) {
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int length = 0;
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int i = 1;
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int[] lps = new int[pattern.length()];
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lps[0] = 0; // LPS for the first character is always 0
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while (i < pattern.length()) {
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if (pattern.charAt(i) == pattern.charAt(length)) {
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length++;
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lps[i] = length;
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i++;
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} else {
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if (length != 0) {
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length = lps[length - 1]; // Fall back to the previous LPS value
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} else {
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lps[i] = 0;
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i++;
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}
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}
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}
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return lps;
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}
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}

‎src/test/java/string/KmpSubstringSearchSnippetTest.java

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/*
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* MIT License
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*
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* Copyright (c) 2017-2024 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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package string;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import org.junit.jupiter.api.Test;
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/*
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* Tests for 30 Seconds of Java code library
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*
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*/
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class KmpSubstringSearchSnippetTest {
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/**
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* Tests for {@link KmpSubstringSearchSnippet#kmpSearch(String, String)}.
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*/
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@Test
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void testKmpSearch() {
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// Test cases for KMP substring search
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assertEquals(6, KmpSubstringSearchSnippet.kmpSearch("abxabcabcaby", "abcaby"));
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assertEquals(7, KmpSubstringSearchSnippet.kmpSearch("subash pandey", "pandey"));
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assertEquals(-1, KmpSubstringSearchSnippet.kmpSearch("abcd", "e"));
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assertEquals(0, KmpSubstringSearchSnippet.kmpSearch("aaaaa", "a"));
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assertEquals(2, KmpSubstringSearchSnippet.kmpSearch("abcdabcd", "cdab"));
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}
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}

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