Bael 7882 (#16500)

* BAEL-7882: Test for finding the index of the smallest number

* BAEL-7882: Added new test cases

* BAEL-7882: Added an example with Apache Commons

core-java-modules/core-java-arrays-operations-basic-2/pom.xml

@@ -13,4 +13,12 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>3.14.0</version>
+        </dependency>
+    </dependencies>
+
 </project>

core-java-modules/core-java-arrays-operations-basic-2/src/test/java/com/baeldung/array/smallestindex/SmallestElementIndexUnitTest.java

@@ -0,0 +1,132 @@
+package com.baeldung.array.smallestindex;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import org.apache.commons.lang3.ArrayUtils;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+class SmallestElementIndexUnitTest {
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingForLoop_thenGetCorrectResult(int[] array, int expectedIndex) {
+        int minValue = Integer.MAX_VALUE;
+        int minIndex = -1;
+        for (int i = 0; i < array.length; i++) {
+            if (array[i] < minValue) {
+                minValue = array[i];
+                minIndex = i;
+            }
+        }
+        assertThat(minIndex).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingForLoopAndLookForIndex_thenGetCorrectResult(int[] array, int expectedIndex) {
+        int minValue = Integer.MAX_VALUE;
+        for (int number : array) {
+            if (number < minValue) {
+                minValue = number;
+            }
+        }
+        int minIndex = -1;
+        for (int i = 0; i < array.length; i++) {
+            if (array[i] == minValue) {
+                minIndex = i;
+                break;
+            }
+        }
+        assertThat(minIndex).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingIntStreamAndLookForIndex_thenGetCorrectResult(int[] array, int expectedIndex) {
+        int minValue = Arrays.stream(array).min().orElse(Integer.MAX_VALUE);
+        int minIndex = -1;
+        for (int i = 0; i < array.length; i++) {
+            if (array[i] == minValue) {
+                minIndex = i;
+                break;
+            }
+        }
+        assertThat(minIndex).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingIntStreamAndLookForIndexWithIntStream_thenGetCorrectResult(int[] array, int expectedIndex) {
+        int minValue = Arrays.stream(array).min().orElse(Integer.MAX_VALUE);
+        int minIndex = IntStream.range(0, array.length)
+          .filter(index -> array[index] == minValue)
+          .findFirst().orElse(-1);
+        assertThat(minIndex).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingIntStreamAndLookForIndexWithArrayUtils_thenGetCorrectResult(int[] array, int expectedIndex) {
+        int minValue = Arrays.stream(array).min().orElse(Integer.MAX_VALUE);
+        int minIndex = ArrayUtils.indexOf(array, minValue);
+        assertThat(minIndex).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("referenceTypesProvider")
+    void givenArray_whenUsingReduce_thenGetCorrectResult(Integer[] array, int expectedIndex) {
+        int minValue = Arrays.stream(array).reduce(Integer.MAX_VALUE, Integer::min);
+        int minIndex = ArrayUtils.indexOf(array, minValue);
+        assertThat(minIndex).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("referenceTypesProvider")
+    void givenArray_whenUsingReduceAndList_thenGetCorrectResult(Integer[] array, int expectedIndex) {
+        List<Integer> list = Arrays.asList(array);
+        int minValue = list.stream().reduce(Integer.MAX_VALUE, Integer::min);
+        int index = list.indexOf(minValue);
+        assertThat(index).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingReduceWithRange_thenGetCorrectResult(int[] array, int expectedIndex) {
+        int index = IntStream.range(0, array.length)
+          .reduce((a, b) -> array[a] <= array[b] ? a : b)
+          .orElse(-1);
+        assertThat(index).isEqualTo(expectedIndex);
+    }
+
+    @ParameterizedTest
+    @MethodSource("primitiveProvider")
+    void givenArray_whenUsingPrimitiveStreams_thenGetCorrectResult(int[] array, int expectedIndex) {
+        List<Integer> list = Arrays.stream(array).boxed().collect(Collectors.toList());
+        int minValue = Arrays.stream(array).min().orElse(Integer.MAX_VALUE);
+        int index = list.indexOf(minValue);
+        assertThat(index).isEqualTo(expectedIndex);
+    }
+
+    static Stream<Arguments> primitiveProvider() {
+        return Stream.of(
+          Arguments.of(new int[]{585, 190, 201, 82, 332}, 3),
+          Arguments.of(new int[]{1, 1, 1}, 0),
+          Arguments.of(new int[]{}, -1)
+        );
+    }
+
+    static Stream<Arguments> referenceTypesProvider() {
+        return Stream.of(
+          Arguments.of(new Integer[]{585, 190, 201, 82, 332}, 3),
+          Arguments.of(new Integer[]{1, 1, 1}, 0),
+          Arguments.of(new Integer[]{}, -1)
+        );
+    }
+}