diff --git a/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java new file mode 100644 index 0000000000..c0962c7079 --- /dev/null +++ b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java @@ -0,0 +1,26 @@ +package com.baeldung.algorithms.topkelements; + +import java.util.ArrayList; +import java.util.List; + +public class BruteForceTopKElementsFinder implements TopKElementsFinder { + + public List findTopK(List input, int k) { + List array = new ArrayList<>(input); + List 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; + } +} diff --git a/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java new file mode 100644 index 0000000000..16ae7f1254 --- /dev/null +++ b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java @@ -0,0 +1,26 @@ +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 { + + public List findTopK(List input, int k) { + PriorityQueue maxHeap = new PriorityQueue<>(); + + input.forEach(number -> { + maxHeap.add(number); + + if (maxHeap.size() > k) { + maxHeap.poll(); + } + }); + + List topKList = new ArrayList<>(maxHeap); + Collections.reverse(topKList); + + return topKList; + } +} diff --git a/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java new file mode 100644 index 0000000000..a9c7881408 --- /dev/null +++ b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java @@ -0,0 +1,7 @@ +package com.baeldung.algorithms.topkelements; + +import java.util.List; + +public interface TopKElementsFinder> { + List findTopK(List input, int k); +} diff --git a/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java new file mode 100644 index 0000000000..0b898df21d --- /dev/null +++ b/algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java @@ -0,0 +1,17 @@ +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 { + + public List findTopK(List input, int k) { + Set sortedSet = new TreeSet<>(Comparator.reverseOrder()); + sortedSet.addAll(input); + + return sortedSet.stream().limit(k).collect(Collectors.toList()); + } +} diff --git a/algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java b/algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java new file mode 100644 index 0000000000..41fa5e067e --- /dev/null +++ b/algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java @@ -0,0 +1,46 @@ +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 bruteForceFinder = new BruteForceTopKElementsFinder(); + private final TopKElementsFinder maxHeapFinder = new MaxHeapTopKElementsFinder(); + private final TopKElementsFinder treeSetFinder = new TreeSetTopKElementsFinder(); + + private final int k = 4; + private final List distinctIntegers = Arrays.asList(1, 2, 3, 9, 7, 6, 12); + private final List distinctIntegersTopK = Arrays.asList(9, 7, 6, 12); + private final List nonDistinctIntegers = Arrays.asList(1, 2, 3, 3, 9, 9, 7, 6, 12); + private final List 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); + } +}