Add SecondMinMax (#4432)

* Added Second Min/Max program

* Clang-format-lint error resolved

* Clang-format-error 2

* Added Program to find Second Minimum/Maximum element

* Test File & few changes

* Clang-lint-error resolved

* Maven Build Error Resolved

* Clang-lint-error resolved

* Clang-lint-error resolved 2

* Changes Resolved

* Test Arguements are Streamed

* Clang-lint-error resolved

* incresed code reusability

* Added Program to find Second Min / Max

* Program to find Second Min / Max

* Program to find Second Minimum / Maximum

* Program to find Second Best Number

* style: mark `initialVal` as `final`

* style: resolve `MultipleVariableDeclarations`

Each variable declaration must be in its own statement.

---------

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

src/main/java/com/thealgorithms/maths/SecondMinMax.java

@@ -0,0 +1,60 @@
+package com.thealgorithms.maths;
+
+import java.util.function.BiPredicate;
+
+public final class SecondMinMax {
+
+    /**
+     * Utility class for finding second maximum or minimum based on BiPredicate
+     * @exception IllegalArgumentException => if input array is of length less than 2 also if all elements are same
+     * @return the second minimum / maximum value from the input array
+     * @author Bharath Sanjeevi ( https://github.com/BharathSanjeeviT )
+     */
+
+    private SecondMinMax() {
+    }
+
+    private static int secondBest(final int[] arr, final int initialVal, final BiPredicate<Integer, Integer> isBetter) {
+        checkInput(arr);
+        int best = initialVal;
+        int secBest = initialVal;
+        for (final int num : arr) {
+            if (isBetter.test(num, best)) {
+                secBest = best;
+                best = num;
+            } else if ((isBetter.test(num, secBest)) && (num != best)) {
+                secBest = num;
+            }
+        }
+        checkOutput(secBest, initialVal);
+        return secBest;
+    }
+
+    /**
+     * @brief Finds the Second minimum / maximum value from the array
+     * @param arr the input array
+     * @exception IllegalArgumentException => if input array is of length less than 2 also if all elements are same
+     * @return the second minimum / maximum value from the input array
+     * @author Bharath Sanjeevi ( https://github.com/BharathSanjeeviT )
+     */
+
+    public static int findSecondMin(final int[] arr) {
+        return secondBest(arr, Integer.MAX_VALUE, (a, b) -> a < b);
+    }
+
+    public static int findSecondMax(final int[] arr) {
+        return secondBest(arr, Integer.MIN_VALUE, (a, b) -> a > b);
+    }
+
+    private static void checkInput(final int[] arr) {
+        if (arr.length < 2) {
+            throw new IllegalArgumentException("Input array must have length of at least two");
+        }
+    }
+
+    private static void checkOutput(final int secNum, final int initialVal) {
+        if (secNum == initialVal) {
+            throw new IllegalArgumentException("Input array should have at least 2 distinct elements");
+        }
+    }
+}

src/test/java/com/thealgorithms/maths/SecondMinMaxTest.java

@@ -0,0 +1,58 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class SecondMinMaxTest {
+
+    private static final String EXP_MSG_ARR_LEN_LESS_2 = "Input array must have length of at least two";
+    private static final String EXP_MSG_ARR_SAME_ELE = "Input array should have at least 2 distinct elements";
+
+    public static class TestCase {
+        public TestCase(final int[] inInputArray, final int inSecondMin, final int inSecondMax) {
+            inputArray = inInputArray;
+            secondMin = inSecondMin;
+            secondMax = inSecondMax;
+        }
+        final int[] inputArray;
+        final int secondMin;
+        final int secondMax;
+    }
+
+    @Test
+    public void testForEmptyInputArray() {
+        IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> SecondMinMax.findSecondMin(new int[] {}));
+        assertEquals(exception.getMessage(), EXP_MSG_ARR_LEN_LESS_2);
+    }
+
+    @Test
+    public void testForArrayWithSingleElement() {
+        IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> SecondMinMax.findSecondMax(new int[] {1}));
+        assertEquals(exception.getMessage(), EXP_MSG_ARR_LEN_LESS_2);
+    }
+
+    @Test
+    public void testForArrayWithSameElements() {
+        IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> SecondMinMax.findSecondMin(new int[] {1, 1, 1, 1}));
+        assertEquals(exception.getMessage(), EXP_MSG_ARR_SAME_ELE);
+    }
+
+    @ParameterizedTest
+    @MethodSource("inputStream")
+    void numberTests(final TestCase tc) {
+        Assertions.assertEquals(tc.secondMax, SecondMinMax.findSecondMax(tc.inputArray));
+        Assertions.assertEquals(tc.secondMin, SecondMinMax.findSecondMin(tc.inputArray));
+    }
+
+    private static Stream<Arguments> inputStream() {
+        return Stream.of(Arguments.of(new TestCase(new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 2, 9)), Arguments.of(new TestCase(new int[] {5, 4, 5, 5, 5}, 5, 4)), Arguments.of(new TestCase(new int[] {-1, 0}, 0, -1)),
+            Arguments.of(new TestCase(new int[] {-10, -9, -8, -7, -6, -5, -4, -3, -2, -1}, -9, -2)), Arguments.of(new TestCase(new int[] {3, -2, 3, 9, -4, -4, 8}, -2, 8)));
+    }
+}