renamed function names and few fixes w.r.t to suggestion

Signed-off-by: JeevaRamanathan <jeevaramanathan.m@infosys.com>

Author: JeevaRamanathan

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

@@ -43,25 +43,28 @@ private Isogram() {
      * @throws IllegalArgumentException if the string contains non-alphabetic
      *                                  characters
      */
-    public static boolean isIsogramByArray(String str) {
+    public static boolean isAlphabeticIsogram(String str) {
         if (str == null || str.isEmpty()) {
             return true;
         }
 
-        String lowerStr = str.toLowerCase();
-        boolean[] seenChars = new boolean[26];
+        str = str.toLowerCase();
 
-        for (int i = 0; i < lowerStr.length(); i++) {
-            char ch = lowerStr.charAt(i);
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            if (ch < 'a' || ch > 'z') {
+                throw new IllegalArgumentException("Input contains non-alphabetic character: '" + ch + "'");
+            }
+        }
 
-            // Check if character is a letter
-            if (ch >= 'a' && ch <= 'z') {
-                int index = ch - 'a';
-                if (seenChars[index]) {
-                    return false; // Letter already seen
-                }
-                seenChars[index] = true;
+        boolean[] seenChars = new boolean[26];
+        for (int i = 0; i < str.length(); i++) {
+            char ch = str.charAt(i);
+            int index = ch - 'a';
+            if (seenChars[index]) {
+                return false;
             }
+            seenChars[index] = true;
         }
         return true;
     }
@@ -74,7 +77,7 @@ public static boolean isIsogramByArray(String str) {
      * @param str the input string
      * @return true if the string is an isogram, false otherwise
      */
-    public static boolean isIsogramByLength(String str) {
+    public static boolean isFullIsogram(String str) {
         if (str == null || str.isEmpty()) {
             return true;
         }

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

@@ -1,6 +1,8 @@
 package com.thealgorithms.strings;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.stream.Stream;
@@ -13,7 +15,7 @@ public class IsogramTest {
     record IsogramTestCase(String input, boolean expected) {
     }
 
-    private static Stream<IsogramTestCase> isogramArrayTestData() {
+    private static Stream<IsogramTestCase> isAlphabeticIsogram() {
         return Stream.of(
             // Valid isograms (only checks letters)
             new IsogramTestCase("uncopyrightable", true), new IsogramTestCase("dermatoglyphics", true), new IsogramTestCase("background", true), new IsogramTestCase("python", true), new IsogramTestCase("keyboard", true), new IsogramTestCase("clipboard", true), new IsogramTestCase("flowchart", true),
@@ -30,7 +32,7 @@ private static Stream<IsogramTestCase> isogramArrayTestData() {
             new IsogramTestCase("Python", true), new IsogramTestCase("BACKGROUND", true), new IsogramTestCase("Hello", false), new IsogramTestCase("PROGRAMMING", false));
     }
 
-    private static Stream<IsogramTestCase> isogramLengthTestData() {
+    private static Stream<IsogramTestCase> isFullIsogram() {
         return Stream.of(
             // Valid isograms (checks all characters)
             new IsogramTestCase("uncopyrightable", true), new IsogramTestCase("dermatoglyphics", true), new IsogramTestCase("background", true), new IsogramTestCase("python", true), new IsogramTestCase("keyboard", true), new IsogramTestCase("clipboard", true), new IsogramTestCase("flowchart", true),
@@ -60,34 +62,56 @@ private static Stream<IsogramTestCase> isogramLengthTestData() {
     }
 
     @ParameterizedTest
-    @MethodSource("isogramArrayTestData")
+    @MethodSource("isAlphabeticIsogram")
     void testIsogramByArray(IsogramTestCase testCase) {
-        assertEquals(testCase.expected(), Isogram.isIsogramByArray(testCase.input()));
+        assertEquals(testCase.expected(), Isogram.isAlphabeticIsogram(testCase.input()));
     }
 
     @ParameterizedTest
-    @MethodSource("isogramLengthTestData")
+    @MethodSource("isFullIsogram")
     void testIsogramByLength(IsogramTestCase testCase) {
-        assertEquals(testCase.expected(), Isogram.isIsogramByLength(testCase.input()));
+        assertEquals(testCase.expected(), Isogram.isFullIsogram(testCase.input()));
     }
 
     @Test
     void testNullInputByArray() {
-        assertTrue(Isogram.isIsogramByArray(null));
+        assertTrue(Isogram.isAlphabeticIsogram(null));
     }
 
     @Test
     void testNullInputByLength() {
-        assertTrue(Isogram.isIsogramByLength(null));
+        assertTrue(Isogram.isFullIsogram(null));
     }
 
     @Test
     void testEmptyStringByArray() {
-        assertTrue(Isogram.isIsogramByArray(""));
+        assertTrue(Isogram.isAlphabeticIsogram(""));
     }
 
     @Test
     void testEmptyStringByLength() {
-        assertTrue(Isogram.isIsogramByLength(""));
+        assertTrue(Isogram.isFullIsogram(""));
+    }
+
+    @Test
+    void testAlphabeticIsogramThrowsException() {
+        // Test that IllegalArgumentException is thrown for non-alphabetic characters
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("1"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("@"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("python!"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("123algorithm"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("hello123"));
+        assertThrows(IllegalArgumentException.class, () -> Isogram.isAlphabeticIsogram("!@@#$%^&*()"));
+    }
+
+    @Test
+    void testFullIsogramWithMixedCharacters() {
+        // Test that full isogram method handles all character types without exceptions
+        assertTrue(Isogram.isFullIsogram("abc123"));
+        assertFalse(Isogram.isFullIsogram("test@email")); // 'e' repeats
+        assertFalse(Isogram.isFullIsogram("hello123")); // 'l' repeats
+        assertTrue(Isogram.isFullIsogram("1234567890"));
+        assertFalse(Isogram.isFullIsogram("12321")); // '1' and '2' repeat
+        assertTrue(Isogram.isFullIsogram("!@#$%^&*()"));
     }
 }