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Add Quick Select (#2860)
Co-authored-by: Nils Goldmann <goldman09@mi.fu-berlin.de> Co-authored-by: Andrii Siriak <siryaka@gmail.com>
This commit is contained in:
Nils-Goldmann
240
src/test/java/com/thealgorithms/searches/QuickSelectTest.java
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240
src/test/java/com/thealgorithms/searches/QuickSelectTest.java
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package com.thealgorithms.searches;
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import org.junit.jupiter.api.Test;
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import java.util.*;
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import java.util.stream.Collectors;
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import static org.junit.jupiter.api.Assertions.*;
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class QuickSelectTest {
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@Test
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void quickSelectMinimumOfOneElement() {
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List<Integer> elements = Collections.singletonList(42);
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int minimum = QuickSelect.select(elements, 0);
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assertEquals(42, minimum);
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}
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@Test
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void quickSelectMinimumOfTwoElements() {
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List<Integer> elements1 = Arrays.asList(42, 90);
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List<Integer> elements2 = Arrays.asList(90, 42);
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int minimum1 = QuickSelect.select(elements1, 0);
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int minimum2 = QuickSelect.select(elements2, 0);
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assertEquals(42, minimum1);
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assertEquals(42, minimum2);
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}
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@Test
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void quickSelectMinimumOfThreeElements() {
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List<Integer> elements1 = Arrays.asList(1, 2, 3);
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List<Integer> elements2 = Arrays.asList(2, 1, 3);
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List<Integer> elements3 = Arrays.asList(2, 3, 1);
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int minimum1 = QuickSelect.select(elements1, 0);
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int minimum2 = QuickSelect.select(elements2, 0);
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int minimum3 = QuickSelect.select(elements3, 0);
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assertEquals(1, minimum1);
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assertEquals(1, minimum2);
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assertEquals(1, minimum3);
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}
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@Test
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void quickSelectMinimumOfManyElements() {
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List<Integer> elements = generateRandomIntegers(NUM_RND_ELEMENTS);
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int actual = QuickSelect.select(elements, 0);
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int expected = elements.stream().min(Comparator.naturalOrder()).get();
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assertEquals(expected, actual);
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}
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@Test
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void quickSelectMaximumOfOneElement() {
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List<Integer> elements = Collections.singletonList(42);
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int maximum = QuickSelect.select(elements, 0);
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assertEquals(42, maximum);
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}
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@Test
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void quickSelectMaximumOfTwoElements() {
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List<Integer> elements1 = Arrays.asList(42, 90);
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List<Integer> elements2 = Arrays.asList(90, 42);
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int maximum1 = QuickSelect.select(elements1, 1);
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int maximum2 = QuickSelect.select(elements2, 1);
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assertEquals(90, maximum1);
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assertEquals(90, maximum2);
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}
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@Test
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void quickSelectMaximumOfThreeElements() {
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List<Integer> elements1 = Arrays.asList(1, 2, 3);
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List<Integer> elements2 = Arrays.asList(2, 1, 3);
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List<Integer> elements3 = Arrays.asList(2, 3, 1);
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int maximum1 = QuickSelect.select(elements1, 2);
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int maximum2 = QuickSelect.select(elements2, 2);
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int maximum3 = QuickSelect.select(elements3, 2);
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assertEquals(3, maximum1);
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assertEquals(3, maximum2);
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assertEquals(3, maximum3);
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}
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@Test
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void quickSelectMaximumOfManyElements() {
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List<Integer> elements = generateRandomIntegers(NUM_RND_ELEMENTS);
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int actual = QuickSelect.select(elements, NUM_RND_ELEMENTS - 1);
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int expected = elements.stream().max(Comparator.naturalOrder()).get();
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assertEquals(expected, actual);
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}
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@Test
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void quickSelectMedianOfOneElement() {
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List<Integer> elements = Collections.singletonList(42);
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int median = QuickSelect.select(elements, 0);
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assertEquals(42, median);
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}
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@Test
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void quickSelectMedianOfThreeElements() {
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List<Integer> elements1 = Arrays.asList(1, 2, 3);
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List<Integer> elements2 = Arrays.asList(2, 1, 3);
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List<Integer> elements3 = Arrays.asList(2, 3, 1);
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int median1 = QuickSelect.select(elements1, 1);
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int median2 = QuickSelect.select(elements2, 1);
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int median3 = QuickSelect.select(elements3, 1);
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assertEquals(2, median1);
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assertEquals(2, median2);
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assertEquals(2, median3);
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}
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@Test
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void quickSelectMedianOfManyElements() {
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int medianIndex = NUM_RND_ELEMENTS / 2;
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List<Integer> elements = generateRandomIntegers(NUM_RND_ELEMENTS);
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int actual = QuickSelect.select(elements, medianIndex);
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List<Integer> elementsSorted = getSortedCopyOfList(elements);
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assertEquals(elementsSorted.get(medianIndex), actual);
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}
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@Test
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void quickSelect30thPercentileOf10Elements() {
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List<Integer> elements = generateRandomIntegers(10);
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int actual = QuickSelect.select(elements, 2);
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List<Integer> elementsSorted = getSortedCopyOfList(elements);
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assertEquals(elementsSorted.get(2), actual);
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}
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@Test
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void quickSelect30thPercentileOfManyElements() {
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int percentile30th = NUM_RND_ELEMENTS / 10 * 3;
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List<Integer> elements = generateRandomIntegers(NUM_RND_ELEMENTS);
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int actual = QuickSelect.select(elements, percentile30th);
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List<Integer> elementsSorted = getSortedCopyOfList(elements);
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assertEquals(elementsSorted.get(percentile30th), actual);
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}
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@Test
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void quickSelect70thPercentileOf10Elements() {
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List<Integer> elements = generateRandomIntegers(10);
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int actual = QuickSelect.select(elements, 6);
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List<Integer> elementsSorted = getSortedCopyOfList(elements);
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assertEquals(elementsSorted.get(6), actual);
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}
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@Test
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void quickSelect70thPercentileOfManyElements() {
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int percentile70th = NUM_RND_ELEMENTS / 10 * 7;
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List<Integer> elements = generateRandomIntegers(NUM_RND_ELEMENTS);
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int actual = QuickSelect.select(elements, percentile70th);
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List<Integer> elementsSorted = getSortedCopyOfList(elements);
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assertEquals(elementsSorted.get(percentile70th), actual);
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}
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@Test
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void quickSelectMedianOfThreeCharacters() {
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List<Character> elements = Arrays.asList('X', 'Z', 'Y');
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char actual = QuickSelect.select(elements, 1);
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assertEquals(actual, 'Y');
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}
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@Test
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void quickSelectMedianOfManyCharacters() {
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List<Character> elements = generateRandomCharacters(NUM_RND_ELEMENTS);
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char actual = QuickSelect.select(elements, NUM_RND_ELEMENTS / 30);
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List<Character> elementsSorted = getSortedCopyOfList(elements);
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assertEquals(elementsSorted.get(NUM_RND_ELEMENTS / 30), actual);
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}
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@Test
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void quickSelectNullList() {
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NullPointerException exception = assertThrows(
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NullPointerException.class,
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() -> QuickSelect.select(null, 0)
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);
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String expectedMsg = "The list of elements must not be null.";
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assertEquals(expectedMsg, exception.getMessage());
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}
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@Test
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void quickSelectEmptyList() {
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List<String> objects = Collections.emptyList();
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IllegalArgumentException exception = assertThrows(
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IllegalArgumentException.class,
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() -> QuickSelect.select(objects, 0)
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);
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String expectedMsg = "The list of elements must not be empty.";
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assertEquals(expectedMsg, exception.getMessage());
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}
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@Test
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void quickSelectIndexOutOfLeftBound() {
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IndexOutOfBoundsException exception = assertThrows(
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IndexOutOfBoundsException.class,
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() -> QuickSelect.select(Collections.singletonList(1), -1)
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);
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String expectedMsg = "The index must not be negative.";
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assertEquals(expectedMsg, exception.getMessage());
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}
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@Test
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void quickSelectIndexOutOfRightBound() {
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IndexOutOfBoundsException exception = assertThrows(
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IndexOutOfBoundsException.class,
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() -> QuickSelect.select(Collections.singletonList(1), 1)
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);
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String expectedMsg = "The index must be less than the number of elements.";
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assertEquals(expectedMsg, exception.getMessage());
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}
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private static final int NUM_RND_ELEMENTS = 99;
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private static final Random RANDOM = new Random(42);
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private static final int ASCII_A = 0x41;
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private static final int ASCII_Z = 0x5A;
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private static List<Integer> generateRandomIntegers(int n) {
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return RANDOM.ints(n).boxed().collect(Collectors.toList());
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}
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private static List<Character> generateRandomCharacters(int n) {
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return RANDOM.ints(n, ASCII_A, ASCII_Z)
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.mapToObj(i -> (char) i)
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.collect(Collectors.toList());
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}
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private static <T extends Comparable<T>> List<T> getSortedCopyOfList(List<T> list) {
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return list.stream().sorted().collect(Collectors.toList());
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}
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}
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