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iaforek
2018-01-28 18:29:38 +00:00
committed by GitHub
parent 2dbb293e66 0d85d1ad01
commit fc3a9264d7
1004 changed files with 233504 additions and 3396 deletions
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algorithms/README.md
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@@ -15,3 +15,4 @@
- [Introduction to JGraphT](http://www.baeldung.com/jgrapht)
- [Introduction to Minimax Algorithm](http://www.baeldung.com/java-minimax-algorithm)
- [How to Calculate Levenshtein Distance in Java?](http://www.baeldung.com/java-levenshtein-distance)
- [How to Find the Kth Largest Element in Java](http://www.baeldung.com/java-kth-largest-element)
algorithms/pom.xml
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@@ -39,6 +39,12 @@
<artifactId>jgrapht-core</artifactId>
<version>1.0.1</version>
</dependency>
<dependency>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
<version>3.9.0</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
algorithms/src/main/java/com/baeldung/algorithms/kthlargest/FindKthLargest.java
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@@ -0,0 +1,111 @@
package com.baeldung.algorithms.kthlargest;
import java.util.Arrays;
import java.util.Collections;
import java.util.stream.IntStream;
public class FindKthLargest {
public int findKthLargestBySorting(Integer[] arr, int k) {
Arrays.sort(arr);
int targetIndex = arr.length - k;
return arr[targetIndex];
}
public int findKthLargestBySortingDesc(Integer[] arr, int k) {
Arrays.sort(arr, Collections.reverseOrder());
return arr[k - 1];
}
public int findKthElementByQuickSelect(Integer[] arr, int left, int right, int k) {
if (k >= 0 && k <= right - left + 1) {
int pos = partition(arr, left, right);
if (pos - left == k) {
return arr[pos];
}
if (pos - left > k) {
return findKthElementByQuickSelect(arr, left, pos - 1, k);
}
return findKthElementByQuickSelect(arr, pos + 1, right, k - pos + left - 1);
}
return 0;
}
public int findKthElementByQuickSelectWithIterativePartition(Integer[] arr, int left, int right, int k) {
if (k >= 0 && k <= right - left + 1) {
int pos = partitionIterative(arr, left, right);
if (pos - left == k) {
return arr[pos];
}
if (pos - left > k) {
return findKthElementByQuickSelectWithIterativePartition(arr, left, pos - 1, k);
}
return findKthElementByQuickSelectWithIterativePartition(arr, pos + 1, right, k - pos + left - 1);
}
return 0;
}
private int partition(Integer[] arr, int left, int right) {
int pivot = arr[right];
Integer[] leftArr;
Integer[] rightArr;
leftArr = IntStream.range(left, right)
.filter(i -> arr[i] < pivot)
.map(i -> arr[i])
.boxed()
.toArray(Integer[]::new);
rightArr = IntStream.range(left, right)
.filter(i -> arr[i] > pivot)
.map(i -> arr[i])
.boxed()
.toArray(Integer[]::new);
int leftArraySize = leftArr.length;
System.arraycopy(leftArr, 0, arr, left, leftArraySize);
arr[leftArraySize + left] = pivot;
System.arraycopy(rightArr, 0, arr, left + leftArraySize + 1, rightArr.length);
return left + leftArraySize;
}
private int partitionIterative(Integer[] arr, int left, int right) {
int pivot = arr[right], i = left;
for (int j = left; j <= right - 1; j++) {
if (arr[j] <= pivot) {
swap(arr, i, j);
i++;
}
}
swap(arr, i, right);
return i;
}
public int findKthElementByRandomizedQuickSelect(Integer[] arr, int left, int right, int k) {
if (k >= 0 && k <= right - left + 1) {
int pos = randomPartition(arr, left, right);
if (pos - left == k) {
return arr[pos];
}
if (pos - left > k) {
return findKthElementByRandomizedQuickSelect(arr, left, pos - 1, k);
}
return findKthElementByRandomizedQuickSelect(arr, pos + 1, right, k - pos + left - 1);
}
return 0;
}
private int randomPartition(Integer arr[], int left, int right) {
int n = right - left + 1;
int pivot = (int) (Math.random()) % n;
swap(arr, left + pivot, right);
return partition(arr, left, right);
}
private void swap(Integer[] arr, int n1, int n2) {
int temp = arr[n2];
arr[n2] = arr[n1];
arr[n1] = temp;
}
}
algorithms/src/test/java/com/baeldung/algorithms/kthlargest/FindKthLargestUnitTest.java
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package com.baeldung.algorithms.kthlargest;
import static org.assertj.core.api.Assertions.*;
import org.junit.Before;
import org.junit.Test;
public class FindKthLargestUnitTest {
private FindKthLargest findKthLargest;
private Integer[] arr = { 3, 7, 1, 2, 8, 10, 4, 5, 6, 9 };
@Before
public void setup() {
findKthLargest = new FindKthLargest();
}
@Test
public void givenIntArray_whenFindKthLargestBySorting_thenGetResult() {
int k = 3;
assertThat(findKthLargest.findKthLargestBySorting(arr, k)).isEqualTo(8);
}
@Test
public void givenIntArray_whenFindKthLargestBySortingDesc_thenGetResult() {
int k = 3;
assertThat(findKthLargest.findKthLargestBySortingDesc(arr, k)).isEqualTo(8);
}
@Test
public void givenIntArray_whenFindKthLargestByQuickSelect_thenGetResult() {
int k = 3;
int kthLargest = arr.length - k;
assertThat(findKthLargest.findKthElementByQuickSelect(arr, 0, arr.length - 1, kthLargest)).isEqualTo(8);
}
@Test
public void givenIntArray_whenFindKthElementByQuickSelectIterative_thenGetResult() {
int k = 3;
int kthLargest = arr.length - k;
assertThat(findKthLargest.findKthElementByQuickSelectWithIterativePartition(arr, 0, arr.length - 1, kthLargest)).isEqualTo(8);
}
@Test
public void givenIntArray_whenFindKthSmallestByQuickSelect_thenGetResult() {
int k = 3;
assertThat(findKthLargest.findKthElementByQuickSelect(arr, 0, arr.length - 1, k - 1)).isEqualTo(3);
}
@Test
public void givenIntArray_whenFindKthLargestByRandomizedQuickSelect_thenGetResult() {
int k = 3;
int kthLargest = arr.length - k;
assertThat(findKthLargest.findKthElementByRandomizedQuickSelect(arr, 0, arr.length - 1, kthLargest)).isEqualTo(8);
}
}