feat: add TitleCase implementation

Author: Rosander0

src/main/java/com/thealgorithms/strings/TitleCase.java

@@ -0,0 +1,54 @@
+package com.thealgorithms.strings;
+
+/**
+ * Title Case converts a string so that the first letter of each word
+ * is capitalized and the rest are lowercase.
+ * Example: "the quick brown fox" -> "The Quick Brown Fox"
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Title_case">
+ *     Wikipedia: Title Case</a>
+ */
+public final class TitleCase {
+
+    private TitleCase() {
+        // Utility class
+    }
+
+    /**
+     * Converts a string to title case.
+     *
+     * @param input The string to convert
+     * @return The title-cased string, or empty string if input is null/empty.
+     *     If input contains only whitespace, it is returned as is.
+     */
+    public static String toTitleCase(final String input) {
+        if (input == null || input.isEmpty()) {
+            return "";
+        }
+
+        StringBuilder result = new StringBuilder(input.length());
+        boolean capitalizeNext = true;
+        for (int i = 0; i < input.length(); i++) {
+            char c = input.charAt(i);
+            if (Character.isWhitespace(c)) {
+                capitalizeNext = true;
+                result.append(c);
+                continue;
+            }
+
+            if (capitalizeNext) {
+                if (Character.isLetter(c)) {
+                    result.append(Character.toUpperCase(c));
+                    capitalizeNext = false;
+                } else {
+                    // Keep capitalizeNext=true so the first *letter* after
+                    // punctuation/digits is capitalized.
+                    result.append(c);
+                }
+            } else {
+                result.append(Character.toLowerCase(c));
+            }
+        }
+        return result.toString();
+    }
+}

src/test/java/com/thealgorithms/strings/TitleCaseTest.java

@@ -0,0 +1,39 @@
+package com.thealgorithms.strings;
+// author: Vraj Prajapati @Rosander0
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class TitleCaseTest {
+
+    @Test
+    public void testNullOrEmptyInputs() {
+        assertEquals("", TitleCase.toTitleCase(null));
+        assertEquals("", TitleCase.toTitleCase(""));
+    }
+
+    @Test
+    public void testSingleWord() {
+        assertEquals("Hello", TitleCase.toTitleCase("hello"));
+        assertEquals("Hello", TitleCase.toTitleCase("HELLO"));
+        assertEquals("A", TitleCase.toTitleCase("a"));
+    }
+
+    @Test
+    public void testMultipleWords() {
+        assertEquals("The Quick Brown Fox", TitleCase.toTitleCase("the quick brown fox"));
+        assertEquals("The Quick Brown Fox", TitleCase.toTitleCase("THE QUICK BROWN FOX"));
+        assertEquals("Already Title Case", TitleCase.toTitleCase("already Title Case"));
+    }
+
+    @Test
+    public void testWhitespace() {
+        assertEquals("  Spaces  ", TitleCase.toTitleCase("  spaces  "));
+    }
+
+    @Test
+    public void testQuotedWords() {
+        assertEquals("\"Hello\"", TitleCase.toTitleCase("\"hello\""));
+    }
+}