Update Pangram.java

Updated the Pangram.java file by adding a bitwise approach and improving code readability

Author: preritasaini1

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

@@ -3,52 +3,55 @@
 import java.util.HashSet;
 
 /**
+ * Checks if a given string is a Pangram (a sentence containing every letter of the alphabet at least once).
  * Wikipedia: https://en.wikipedia.org/wiki/Pangram
  */
 public final class Pangram {
+
     private Pangram() {
     }
 
     /**
-     * Test code
+     * Main method to test all pangram-checking methods.
      */
     public static void main(String[] args) {
         assert isPangram("The quick brown fox jumps over the lazy dog");
         assert !isPangram("The quick brown fox jumps over the azy dog"); // L is missing
         assert !isPangram("+-1234 This string is not alphabetical");
         assert !isPangram("\u0000/\\");
+        assert isPangramUsingBitwise("The quick brown fox jumps over the lazy dog");
+        assert !isPangramUsingBitwise("Hello, World!");
     }
 
     /**
-     * Checks if a String is considered a Pangram
+     * Checks if a String is a Pangram using a HashSet to track unique characters.
      *
      * @param s The String to check
      * @return {@code true} if s is a Pangram, otherwise {@code false}
      */
-    // alternative approach using Java Collection Framework
     public static boolean isPangramUsingSet(String s) {
-        HashSet<Character> alpha = new HashSet<>();
-        s = s.trim().toLowerCase();
-        for (int i = 0; i < s.length(); i++) {
-            if (s.charAt(i) != ' ') {
-                alpha.add(s.charAt(i));
+        HashSet<Character> uniqueChars = new HashSet<>();
+        s = s.toLowerCase();
+        for (char c : s.toCharArray()) {
+            if (c >= 'a' && c <= 'z') {
+                uniqueChars.add(c);
             }
         }
-        return alpha.size() == 26;
+        return uniqueChars.size() == 26;
     }
 
     /**
-     * Checks if a String is considered a Pangram
+     * Checks if a String is a Pangram by tracking occurrences of each letter in an array.
      *
      * @param s The String to check
      * @return {@code true} if s is a Pangram, otherwise {@code false}
      */
     public static boolean isPangram(String s) {
         boolean[] lettersExisting = new boolean[26];
+        s = s.toLowerCase();
         for (char c : s.toCharArray()) {
-            int letterIndex = c - (Character.isUpperCase(c) ? 'A' : 'a');
-            if (letterIndex >= 0 && letterIndex < lettersExisting.length) {
-                lettersExisting[letterIndex] = true;
+            if (c >= 'a' && c <= 'z') {
+                lettersExisting[c - 'a'] = true;
             }
         }
         for (boolean letterFlag : lettersExisting) {
@@ -60,7 +63,7 @@ public static boolean isPangram(String s) {
     }
 
     /**
-     * Checks if a String is Pangram or not by checking if each alhpabet is present or not
+     * Checks if a String is a Pangram by checking each letter in the alphabet individually.
      *
      * @param s The String to check
      * @return {@code true} if s is a Pangram, otherwise {@code false}
@@ -69,12 +72,32 @@ public static boolean isPangram2(String s) {
         if (s.length() < 26) {
             return false;
         }
-        s = s.toLowerCase(); // Converting s to Lower-Case
+        s = s.toLowerCase();
         for (char i = 'a'; i <= 'z'; i++) {
             if (s.indexOf(i) == -1) {
-                return false; // if any alphabet is not present, return false
+                return false; // if any alphabet is missing, return false
             }
         }
         return true;
     }
+
+    /**
+     * Optimized Pangram check using Bitwise operations.
+     * Each bit in a 32-bit integer represents a unique letter from 'a' to 'z'.
+     *
+     * @param s The String to check
+     * @return {@code true} if s is a Pangram, otherwise {@code false}
+     */
+    public static boolean isPangramUsingBitwise(String s) {
+        int checker = 0;
+        s = s.toLowerCase();
+        for (char c : s.toCharArray()) {
+            if (c >= 'a' && c <= 'z') {
+                int bitIndex = c - 'a';
+                checker |= (1 << bitIndex);
+            }
+        }
+        // If all 26 bits are set, checker will equal 0b11111111111111111111111111 (26 ones)
+        return checker == (1 << 26) - 1;
+    }
 }