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Merge pull request #64 from eugenp/master 

update
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Maiklins 2020-07-15 22:31:02 +02:00 committed by GitHub
parent c3baa7b0a3 6ebf84fcb8
commit 9bb378605d
5 changed files with 122 additions and 0 deletions
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26
algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java Normal file
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package com.baeldung.algorithms.topkelements;
import java.util.ArrayList;
import java.util.List;
public class BruteForceTopKElementsFinder implements TopKElementsFinder<Integer> {
public List<Integer> findTopK(List<Integer> input, int k) {
List<Integer> array = new ArrayList<>(input);
List<Integer> topKList = new ArrayList<>();
for (int i = 0; i < k; i++) {
int maxIndex = 0;
for (int j = 1; j < array.size(); j++) {
if (array.get(j) > array.get(maxIndex)) {
maxIndex = j;
}
}
topKList.add(array.remove(maxIndex));
}
return topKList;
}
}

26
algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java Normal file
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package com.baeldung.algorithms.topkelements;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.PriorityQueue;
public class MaxHeapTopKElementsFinder implements TopKElementsFinder<Integer> {
public List<Integer> findTopK(List<Integer> input, int k) {
PriorityQueue<Integer> maxHeap = new PriorityQueue<>();
input.forEach(number -> {
maxHeap.add(number);
if (maxHeap.size() > k) {
maxHeap.poll();
}
});
List<Integer> topKList = new ArrayList<>(maxHeap);
Collections.reverse(topKList);
return topKList;
}
}

7
algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java Normal file
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package com.baeldung.algorithms.topkelements;
import java.util.List;
public interface TopKElementsFinder<T extends Comparable<T>> {
List<T> findTopK(List<T> input, int k);
}

17
algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java Normal file
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package com.baeldung.algorithms.topkelements;
import java.util.Comparator;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import java.util.stream.Collectors;
public class TreeSetTopKElementsFinder implements TopKElementsFinder<Integer> {
public List<Integer> findTopK(List<Integer> input, int k) {
Set<Integer> sortedSet = new TreeSet<>(Comparator.reverseOrder());
sortedSet.addAll(input);
return sortedSet.stream().limit(k).collect(Collectors.toList());
}
}

46
algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java Normal file
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package com.baeldung.algorithms.topkelements;
import org.junit.Test;
import java.util.Arrays;
import java.util.List;
import static org.assertj.core.api.Java6Assertions.assertThat;
public class TopKElementsFinderUnitTest {
private final TopKElementsFinder<Integer> bruteForceFinder = new BruteForceTopKElementsFinder();
private final TopKElementsFinder<Integer> maxHeapFinder = new MaxHeapTopKElementsFinder();
private final TopKElementsFinder<Integer> treeSetFinder = new TreeSetTopKElementsFinder();
private final int k = 4;
private final List<Integer> distinctIntegers = Arrays.asList(1, 2, 3, 9, 7, 6, 12);
private final List<Integer> distinctIntegersTopK = Arrays.asList(9, 7, 6, 12);
private final List<Integer> nonDistinctIntegers = Arrays.asList(1, 2, 3, 3, 9, 9, 7, 6, 12);
private final List<Integer> nonDistinctIntegersTopK = Arrays.asList(9, 9, 7, 12);
@Test
public void givenArrayDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
assertThat(bruteForceFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
}
@Test
public void givenArrayDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
assertThat(maxHeapFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
}
@Test
public void givenArrayDistinctIntegers_whenTreeSetFindTopK_thenReturnKLargest() {
assertThat(treeSetFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
}
@Test
public void givenArrayNonDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
assertThat(bruteForceFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
}
@Test
public void givenArrayNonDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
assertThat(maxHeapFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
}
}