feat: add WaveSort (#5252)

* Implementing WaveSort Algorithm

* Refactor: Tests to ParameterizedTest

* Checkstyle: Fix wrong align

* Checkstyle: Fix wrong align for second line

* Checkstyle: Remove redundant line

* Naming: fix method name

* Documentation: adding links

* Fix: adding test for isWaveSorted method

* Documentation: adding description for WaveSort

* Testing: test wave sort assert

* Checkstyle: remove redundant whitespace

* Checkstyle: remove redundant newline

* Testing: improving tests

---------

Co-authored-by: alxklm <alx@alx.com>
Co-authored-by: vil02 <65706193+vil02@users.noreply.github.com>

DIRECTORY.md

@@ -528,6 +528,7 @@
             * [TopologicalSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/TopologicalSort.java)
             * [TreeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/TreeSort.java)
             * [WiggleSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/WiggleSort.java)
+            * [WaveSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/WaveSort.java)
           * stacks
             * [BalancedBrackets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/BalancedBrackets.java)
             * [DecimalToAnyUsingStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DecimalToAnyUsingStack.java)
@@ -885,6 +886,7 @@
             * [TopologicalSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/TopologicalSortTest.java)
             * [TreeSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/TreeSortTest.java)
             * [WiggleSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/WiggleSortTest.java)
+            * [WaveSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/WaveSortTest.java)
           * stacks
             * [StackPostfixNotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/StackPostfixNotationTest.java)
           * strings

src/main/java/com/thealgorithms/sorts/WaveSort.java

@@ -0,0 +1,46 @@
+package com.thealgorithms.sorts;
+
+/**
+ * The WaveSort algorithm sorts an array so that every alternate element is greater than its adjacent elements.
+ * This implementation also provides a method to check if an array is wave sorted.
+ */
+public class WaveSort implements SortAlgorithm {
+    /**
+     * Sorts the given array such that every alternate element is greater than its adjacent elements.
+     *
+     * @param array The array to be sorted.
+     * @param <T> The type of elements in the array, which must be Comparable.
+     * @return The sorted array.
+     */
+    @Override
+    public <T extends Comparable<T>> T[] sort(T[] array) {
+        for (int i = 0; i < array.length; i += 2) {
+            if (i > 0 && SortUtils.less(array[i], array[i - 1])) {
+                SortUtils.swap(array, i, i - 1);
+            }
+            if (i < array.length - 1 && SortUtils.less(array[i], array[i + 1])) {
+                SortUtils.swap(array, i, i + 1);
+            }
+        }
+        return array;
+    }
+
+    /**
+     * Checks if the given array is wave sorted. An array is wave sorted if every alternate element is greater than its adjacent elements.
+     *
+     * @param array The array to check.
+     * @param <T> The type of elements in the array, which must be Comparable.
+     * @return true if the array is wave sorted, false otherwise.
+     */
+    public <T extends Comparable<T>> boolean isWaveSorted(T[] array) {
+        for (int i = 0; i < array.length; i += 2) {
+            if (i > 0 && SortUtils.less(array[i], array[i - 1])) {
+                return false;
+            }
+            if (i < array.length - 1 && SortUtils.less(array[i], array[i + 1])) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

src/test/java/com/thealgorithms/sorts/WaveSortTest.java

@@ -0,0 +1,48 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class WaveSortTest {
+    @ParameterizedTest
+    @MethodSource("arraysToWaveSort")
+    public void waveSortTest(Integer[] array) {
+        WaveSort waveSort = new WaveSort();
+        final var inputHistogram = getHistogram(array);
+        final var sortedArray = waveSort.sort(array);
+        assertTrue(waveSort.isWaveSorted(sortedArray));
+        final var sortedHistogram = getHistogram(sortedArray);
+        assertEquals(inputHistogram, sortedHistogram, "Element counts do not match");
+    }
+
+    private Map<Integer, Integer> getHistogram(Integer[] array) {
+        Map<Integer, Integer> histogram = new HashMap<>();
+        for (final var element : array) {
+            histogram.put(element, histogram.getOrDefault(element, 0) + 1);
+        }
+        return histogram;
+    }
+
+    private static Stream<Object[]> arraysToWaveSort() {
+        return Stream.of(new Object[] {new Integer[] {7, 7, 11, 3, 4, 5, 15}}, new Object[] {new Integer[] {1, 2, 3, 4, 5, 6, 7, 8}}, new Object[] {new Integer[] {8, 7, 6, 5, 4, 3, 2, 1}}, new Object[] {new Integer[] {3, 3, 3, 3}}, new Object[] {new Integer[] {-1, -3, -2, -4, -6, -5}},
+            new Object[] {new Integer[] {5, 3, 1, 2, 9, 7, 6, 8, 4, 0}}, new Object[] {new Integer[] {1}}, new Object[] {new Integer[] {2, 1}}, new Object[] {new Integer[] {1, 2}}, new Object[] {new Integer[] {}}, new Object[] {new Integer[] {0, 5, -3, 2, -1, 4, -2, 1, 3}});
+    }
+
+    @ParameterizedTest
+    @MethodSource("waveSortedArrays")
+    public <T extends Comparable<T>> void testIsWaveSorted(T[] array, boolean expected) {
+        final WaveSort waveSort = new WaveSort();
+        assertEquals(expected, waveSort.isWaveSorted(array));
+    }
+    public static Stream<Object[]> waveSortedArrays() {
+        return Stream.of(new Object[] {new Integer[] {3, 1, 4, 2, 5}, Boolean.TRUE}, new Object[] {new Integer[] {3, 1, 4, 2}, Boolean.TRUE}, new Object[] {new Integer[] {1, 3, 2, 4, 5}, Boolean.FALSE}, new Object[] {new Integer[] {4, 3, 5, 2, 3, 1, 2}, Boolean.TRUE},
+            new Object[] {new Integer[] {10, 90, 49, 2, 1, 5, 23}, Boolean.FALSE}, new Object[] {new Integer[] {}, Boolean.TRUE}, new Object[] {new Integer[] {1}, Boolean.TRUE}, new Object[] {new Integer[] {2, 1}, Boolean.TRUE}, new Object[] {new Integer[] {4, 3, 2, 5}, Boolean.FALSE},
+            new Object[] {new Double[] {4.0, 3.0, 5.1, 2.1, 3.3, 1.1, 2.2}, Boolean.TRUE}, new Object[] {new Double[] {10.1, 2.0, 2.0}, Boolean.TRUE}, new Object[] {new String[] {"a", "b", "c", "d"}, Boolean.FALSE}, new Object[] {new String[] {"b", "a", "b", "a", "b"}, Boolean.TRUE});
+    }
+}