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Merge pull request #16018 from Imranalam28/master 

[BAEL-7527] Find Peak Elements of a List
This commit is contained in:
Dominique Plante 2024-03-21 15:59:09 -07:00 committed by GitHub
parent 53b3bca14d b09f501333
commit 0248e55803
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6 changed files with 215 additions and 0 deletions
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40
core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/peakelements/MultiplePeakFinder.java Normal file
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package com.baeldung.peakelements;
import java.util.ArrayList;
import java.util.List;
public class MultiplePeakFinder {
public static List<Integer> findPeaks(int[] arr) {
List<Integer> peaks = new ArrayList<>();
if (arr == null || arr.length == 0) {
return peaks;
}
findPeakElements(arr, 0, arr.length - 1, peaks, arr.length);
return peaks;
}
private static void findPeakElements(int[] arr, int low, int high, List<Integer> peaks, int length) {
if (low > high) {
return;
}
int mid = low + (high - low) / 2;
boolean isPeak = (mid == 0 || arr[mid] > arr[mid - 1]) && (mid == length - 1 || arr[mid] > arr[mid + 1]);
boolean isFirstInSequence = mid > 0 && arr[mid] == arr[mid - 1] && arr[mid] > arr[mid + 1];
if (isPeak || isFirstInSequence) {
if (!peaks.contains(arr[mid])) {
peaks.add(arr[mid]);
}
}
findPeakElements(arr, low, mid - 1, peaks, length);
findPeakElements(arr, mid + 1, high, peaks, length);
}
}

44
core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/peakelements/PeakElementFinder.java Normal file
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package com.baeldung.peakelements;
import java.util.ArrayList;
import java.util.List;
public class PeakElementFinder {
public List<Integer> findPeakElements(int[] arr) {
int n = arr.length;
List<Integer> peaks = new ArrayList<>();
if (n == 0) {
return peaks;
}
for (int i = 0; i < n; i++) {
if (isPeak(arr, i, n)) {
peaks.add(arr[i]);
}
while (i < n - 1 && arr[i] == arr[i + 1]) {
i++;
}
}
return peaks;
}
private boolean isPeak(int[] arr, int index, int n) {
if (index == 0) {
return n > 1 ? arr[index] >= arr[index + 1] : true;
} else if (index == n - 1) {
return arr[index] >= arr[index - 1];
} else if (arr[index] == arr[index + 1] && arr[index] > arr[index - 1]) {
int i = index;
while (i < n - 1 && arr[i] == arr[i + 1]) {
i++;
}
return i == n - 1 || arr[i] > arr[i + 1];
} else {
return arr[index] >= arr[index - 1] && arr[index] >= arr[index + 1];
}
}
}

30
core-java-modules/core-java-collections-array-list-2/src/main/java/com/baeldung/peakelements/SinglePeakFinder.java Normal file
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package com.baeldung.peakelements;
import java.util.OptionalInt;
public class SinglePeakFinder {
public static OptionalInt findSinglePeak(int[] arr) {
int n = arr.length;
if (n < 2) {
return n == 0 ? OptionalInt.empty() : OptionalInt.of(arr[0]);
}
if (arr[0] >= arr[1]) {
return OptionalInt.of(arr[0]);
}
for (int i = 1; i < n - 1; i++) {
if (arr[i] >= arr[i - 1] && arr[i] >= arr[i + 1]) {
return OptionalInt.of(arr[i]);
}
}
if (arr[n - 1] >= arr[n - 2]) {
return OptionalInt.of(arr[n - 1]);
}
return OptionalInt.empty();
}
}

23
core-java-modules/core-java-collections-array-list-2/src/test/java/com/baeldung/peakelements/MultiplePeakFinderUnitTest.java Normal file
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package com.baeldung.peakelements;
import org.junit.jupiter.api.Test;
import java.util.List;
import static org.junit.jupiter.api.Assertions.*;
public class MultiplePeakFinderUnitTest {
@Test
void findPeaks_givenArrayOfIntegers_whenValidInput_thenReturnsCorrectPeaks() {
MultiplePeakFinder finder = new MultiplePeakFinder();
int[] array = {1, 13, 7, 0, 4, 1, 4, 45, 50};
List<Integer> peaks = finder.findPeaks(array);
assertEquals(3, peaks.size());
assertTrue(peaks.contains(4));
assertTrue(peaks.contains(13));
assertTrue(peaks.contains(50));
}
}

46
core-java-modules/core-java-collections-array-list-2/src/test/java/com/baeldung/peakelements/PeakElementFinderUnitTest.java Normal file
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package com.baeldung.peakelements;
import org.junit.jupiter.api.Test;
import java.util.List;
import static org.junit.jupiter.api.Assertions.*;
public class PeakElementFinderUnitTest {
@Test
void findPeakElement_givenArrayOfIntegers_whenValidInput_thenReturnsCorrectPeak() {
PeakElementFinder finder = new PeakElementFinder();
int[] array = {1, 2, 3, 2, 1};
List<Integer> peaks = finder.findPeakElements(array);
assertEquals(1, peaks.size());
assertTrue(peaks.contains(3));
}
@Test
void findPeakElement_givenArrayOfIntegers_whenNoPeaks_thenReturnsEmptyList() {
PeakElementFinder finder = new PeakElementFinder();
int[] array = {};
List<Integer> peaks = finder.findPeakElements(array);
assertEquals(0, peaks.size());
}
@Test
void findPeakElement_givenArrayOfIntegers_whenPeaksAtExtremes_thenReturnsCorrectPeak() {
PeakElementFinder finder = new PeakElementFinder();
int[] array = {5, 2, 1, 3, 4};
List<Integer> peaks = finder.findPeakElements(array);
assertEquals(2, peaks.size());
assertTrue(peaks.contains(5));
assertTrue(peaks.contains(4));
}
@Test
void findPeakElement_givenArrayOfIntegers_whenPlateaus_thenReturnsCorrectPeak() {
PeakElementFinder finder = new PeakElementFinder();
int[] array = {1, 2, 2, 2, 3, 4, 5};
List<Integer> peaks = finder.findPeakElements(array);
assertEquals(1, peaks.size());
assertTrue(peaks.contains(5));
}
}

32
core-java-modules/core-java-collections-array-list-2/src/test/java/com/baeldung/peakelements/SinglePeakFinderUnitTest.java Normal file
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package com.baeldung.peakelements;
import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertTrue;
import java.util.OptionalInt;
public class SinglePeakFinderUnitTest {
@Test
void findSinglePeak_givenArrayOfIntegers_whenValidInput_thenReturnsCorrectPeak() {
int[] arr = {0, 10, 2, 4, 5, 1};
OptionalInt peak = SinglePeakFinder.findSinglePeak(arr);
assertTrue(peak.isPresent());
assertEquals(10, peak.getAsInt());
}
@Test
void findSinglePeak_givenEmptyArray_thenReturnsEmptyOptional() {
int[] arr = {};
OptionalInt peak = SinglePeakFinder.findSinglePeak(arr);
assertTrue(peak.isEmpty());
}
@Test
void findSinglePeak_givenEqualElementArray_thenReturnsCorrectPeak() {
int[] arr = {-2, -2, -2, -2, -2};
OptionalInt peak = SinglePeakFinder.findSinglePeak(arr);
assertTrue(peak.isPresent());
assertEquals(-2, peak.getAsInt());
}
}