rename MAP_OF_CHARS to KEYPAD

Author: Samuel Facchinello

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

@@ -8,7 +8,7 @@
 public final class LetterCombinationsOfPhoneNumber {
 
     // Mapping of numbers to corresponding letters on a phone keypad
-    private static final Map<Integer, String> MAP_OF_CHARS = Map.of(0, "", 1, "", 2, "abc", 3, "def", 4, "ghi", 5, "jkl", 6, "mno", 7, "pqrs", 8, "tuv", 9, "wxyz");
+    private static final Map<Integer, String> KEYPAD = Map.of(0, "", 1, "", 2, "abc", 3, "def", 4, "ghi", 5, "jkl", 6, "mno", 7, "pqrs", 8, "tuv", 9, "wxyz");
 
     private LetterCombinationsOfPhoneNumber() {
     }
@@ -42,7 +42,7 @@ private static List<String> generateCombinations(int[] numbers, int index, Strin
         }
 
         List<String> combinations = new ArrayList<>();
-        final String letters = MAP_OF_CHARS.get(numbers[index]); // Get corresponding letters for the current number
+        final String letters = KEYPAD.get(numbers[index]); // Get corresponding letters for the current number
 
         // Iterate over each letter and recurse to generate further combinations
         for (char letter : letters.toCharArray()) {