Cleanup BoyerMoore (TheAlgorithms#4951)

* modify code to make use of java Optional class * revert changes * add java.util.Optional<Integer> * add java.util.Optional * refactors: make `findmajor` return `optional` * refactors: make method name findMajor and split it * refactors: change method name in tests * Apply suggestions from code review Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com> * change back to int * fix: swap arguments * tests: add some test cases * refactor: add `isMajority` and avoid rounding * style: use `var` * style: swap arguments of `countOccurrences` --------- Co-authored-by: vil02 <vil02@o2.pl> Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

Author: prathameshpowar1910

src/main/java/com/thealgorithms/others/BoyerMoore.java

@@ -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;
  }
 }

src/test/java/com/thealgorithms/others/BoyerMooreTest.java

@@ -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[] {}));
  }
 }