refactor: DecimalToHexadecimal (#5337)

Author: alxkm

src/main/java/com/thealgorithms/conversions/DecimalToHexaDecimal.java

@@ -0,0 +1,42 @@
+package com.thealgorithms.conversions;
+
+/**
+ * This class provides a method to convert a decimal number to a hexadecimal string.
+ */
+final class DecimalToHexadecimal {
+    private static final int SIZE_OF_INT_IN_HALF_BYTES = 8;
+    private static final int NUMBER_OF_BITS_IN_HALF_BYTE = 4;
+    private static final int HALF_BYTE_MASK = 0x0F;
+    private static final char[] HEX_DIGITS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
+
+    private DecimalToHexadecimal() {
+    }
+
+    /**
+     * Converts a decimal number to a hexadecimal string.
+     * @param decimal the decimal number to convert
+     * @return the hexadecimal representation of the decimal number
+     */
+    public static String decToHex(int decimal) {
+        StringBuilder hexBuilder = new StringBuilder(SIZE_OF_INT_IN_HALF_BYTES);
+        for (int i = SIZE_OF_INT_IN_HALF_BYTES - 1; i >= 0; --i) {
+            int currentHalfByte = decimal & HALF_BYTE_MASK;
+            hexBuilder.insert(0, HEX_DIGITS[currentHalfByte]);
+            decimal >>= NUMBER_OF_BITS_IN_HALF_BYTE;
+        }
+        return removeLeadingZeros(hexBuilder.toString().toLowerCase());
+    }
+
+    private static String removeLeadingZeros(String str) {
+        if (str == null || str.isEmpty()) {
+            return str;
+        }
+
+        int i = 0;
+        while (i < str.length() && str.charAt(i) == '0') {
+            i++;
+        }
+
+        return i == str.length() ? "0" : str.substring(i);
+    }
+}

src/main/java/com/thealgorithms/conversions/DecimalToHexadecimal.java

@@ -0,0 +1,14 @@
+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+public class DecimalToHexadecimalTest {
+    @ParameterizedTest
+    @CsvSource({"0, 0", "1, 1", "10, a", "15, f", "16, 10", "255, ff", "190, be", "1800, 708"})
+    void testDecToHex(int decimal, String expectedHex) {
+        assertEquals(expectedHex, DecimalToHexadecimal.decToHex(decimal));
+    }
+}