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Cleanup BoyerMoore #4951

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Merged
merged 14 commits into from
Oct 31, 2023
Merged

Cleanup BoyerMoore #4951

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225a49e
modify code to make use of java Optional class
prathameshpowar1910 Oct 31, 2023
353125d
revert changes
prathameshpowar1910 Oct 31, 2023
0527c59
add java.util.Optional<Integer>
prathameshpowar1910 Oct 31, 2023
286c042
add java.util.Optional
prathameshpowar1910 Oct 31, 2023
fe687c3
refactors: make `findmajor` return `optional`
vil02 Oct 31, 2023
59bbeb1
refactors: make method name findMajor and split it
prathameshpowar1910 Oct 31, 2023
199207d
refactors: change method name in tests
prathameshpowar1910 Oct 31, 2023
1c529e3
Apply suggestions from code review
prathameshpowar1910 Oct 31, 2023
8d17984
change back to int
prathameshpowar1910 Oct 31, 2023
33dd9ec
fix: swap arguments
vil02 Oct 31, 2023
448f568
tests: add some test cases
vil02 Oct 31, 2023
becbb02
refactor: add `isMajority` and avoid rounding
vil02 Oct 31, 2023
4864fc5
style: use `var`
vil02 Oct 31, 2023
6457289
style: swap arguments of `countOccurrences`
vil02 Oct 31, 2023
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35 changes: 25 additions & 10 deletions src/main/java/com/thealgorithms/others/BoyerMoore.java
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Original file line number Diff line number Diff line change
Expand Up @@ -5,35 +5,50 @@
https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_majority_vote_algorithm
*/
package com.thealgorithms.others;
import java.util.Optional;

public final class BoyerMoore {
private BoyerMoore() {
}

public static int findmajor(final int[] a) {
public static Optional<Integer> findMajor(final int[] a) {
final var candidate = findCandidate(a);
final var count = countOccurrences(candidate, a);
if (isMajority(count, a.length)) {
return Optional.of(candidate);
}
return Optional.empty();
}

private static int findCandidate(final int[] a) {
int count = 0;
int cand = -1;
int candidate = -1;
for (final var k : a) {
if (count == 0) {
cand = k;
candidate = k;
count = 1;
} else {
if (k == cand) {
if (k == candidate) {
count++;
} else {
count--;
}
}
}
count = 0;
return candidate;
}

private static int countOccurrences(final int candidate, final int[] a) {
int count = 0;
for (final var j : a) {
if (j == cand) {
if (j == candidate) {
count++;
}
}
if (count > (a.length / 2)) {
return cand;
}
return -1;
return count;
}

private static boolean isMajority(final int count, final int totalCount) {
return 2 * count > totalCount;
}
}
20 changes: 15 additions & 5 deletions src/test/java/com/thealgorithms/others/BoyerMooreTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -11,12 +11,22 @@
public class BoyerMooreTest {

@ParameterizedTest
@MethodSource("inputStream")
void numberTests(int expected, int[] input) {
Assertions.assertEquals(expected, BoyerMoore.findmajor(input));
@MethodSource("inputStreamWithExistingMajority")
void checkWhenMajorityExists(int expected, int[] input) {
Assertions.assertEquals(expected, BoyerMoore.findMajor(input).get());
}

private static Stream<Arguments> inputStream() {
return Stream.of(Arguments.of(5, new int[] {5, 5, 5, 2}), Arguments.of(10, new int[] {10, 10, 20}), Arguments.of(10, new int[] {10, 20, 10}), Arguments.of(10, new int[] {20, 10, 10}), Arguments.of(-1, new int[] {10, 10, 20, 20, 30, 30}), Arguments.of(4, new int[] {1, 4, 2, 4, 4, 5, 4}));
private static Stream<Arguments> inputStreamWithExistingMajority() {
return Stream.of(Arguments.of(5, new int[] {5, 5, 5, 2}), Arguments.of(10, new int[] {10, 10, 20}), Arguments.of(10, new int[] {10, 20, 10}), Arguments.of(10, new int[] {20, 10, 10}), Arguments.of(4, new int[] {1, 4, 2, 4, 4, 5, 4}), Arguments.of(-1, new int[] {-1}));
}

@ParameterizedTest
@MethodSource("inputStreamWithoutMajority")
void checkWhenMajorityExists(int[] input) {
Assertions.assertFalse(BoyerMoore.findMajor(input).isPresent());
}

private static Stream<Arguments> inputStreamWithoutMajority() {
return Stream.of(Arguments.of(new int[] {10, 10, 20, 20, 30, 30}), Arguments.of(new int[] {10, 20, 30, 40, 50}), Arguments.of(new int[] {1, 2}), Arguments.of(new int[] {}));
}
}