Skip to content
Merged
Show file tree
Hide file tree
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
58 changes: 58 additions & 0 deletions src/main/java/com/thealgorithms/searches/BoyerMoore.java
Original file line number Diff line number Diff line change
@@ -0,0 +1,58 @@
package com.thealgorithms.searches;

/**
* Boyer-Moore string search algorithm.
* Efficient algorithm for substring search.
* https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_string-search_algorithm
*/
public class BoyerMoore {

private final int radix; // Radix (number of possible characters)
private final int[] right; // Bad character rule table
private final String pattern;

public BoyerMoore(String pat) {
this.pattern = pat;
this.radix = 256;
this.right = new int[radix];

for (int c = 0; c < radix; c++) {
right[c] = -1;
}

for (int j = 0; j < pat.length(); j++) {
right[pat.charAt(j)] = j;
}
}

public int search(String text) {
if (pattern.isEmpty()) {
return 0;
}

int m = pattern.length();
int n = text.length();

int skip;
for (int i = 0; i <= n - m; i += skip) {
skip = 0;
for (int j = m - 1; j >= 0; j--) {
char txtChar = text.charAt(i + j);
char patChar = pattern.charAt(j);
if (patChar != txtChar) {
skip = Math.max(1, j - right[txtChar]);
break;
}
}
if (skip == 0) {
return i; // Match found
}
}

return -1; // No match
}

public static int staticSearch(String text, String pattern) {
return new BoyerMoore(pattern).search(text);
}
}
55 changes: 55 additions & 0 deletions src/test/java/com/thealgorithms/searches/BoyerMooreTest.java
Original file line number Diff line number Diff line change
@@ -0,0 +1,55 @@
package com.thealgorithms.searches;

import static org.junit.jupiter.api.Assertions.assertEquals;

import org.junit.jupiter.api.Test;

public class BoyerMooreTest {

@Test
public void testPatternFound() {
BoyerMoore bm = new BoyerMoore("ABCDABD");
String text = "ABC ABCDAB ABCDABCDABDE";
int index = bm.search(text);
assertEquals(15, index);
}

@Test
public void testPatternNotFound() {
BoyerMoore bm = new BoyerMoore("XYZ");
String text = "ABC ABCDAB ABCDABCDABDE";
int index = bm.search(text);
assertEquals(-1, index);
}

@Test
public void testPatternAtBeginning() {
BoyerMoore bm = new BoyerMoore("ABC");
String text = "ABCDEF";
int index = bm.search(text);
assertEquals(0, index);
}

@Test
public void testPatternAtEnd() {
BoyerMoore bm = new BoyerMoore("CDE");
String text = "ABCDEFGCDE";
int index = bm.search(text);
assertEquals(2, index); // Primera ocurrencia de "CDE"
}

@Test
public void testEmptyPattern() {
BoyerMoore bm = new BoyerMoore("");
String text = "Hello world";
int index = bm.search(text);
assertEquals(0, index);
}

@Test
public void testStaticSearchMethod() {
String text = "ABCDEFGCDE";
int index = BoyerMoore.staticSearch(text, "CDE");
assertEquals(2, index); // Primera ocurrencia de "CDE"
}
}