Update Pangram.java using Java Collections (#4479)

* Update Pangram.java using Java Collections

A simple separate function isPangramOrNot(String s) has been created which implements the Pangram checking of a string using Java Collection Framework approach.

* Update Pangram.java using Java Collections

* Updated some linting errors in Pangram.java

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

Co-authored-by: Debasish Biswas <debasishbsws.dev@gmail.com>

* Updated Pangram.java

Method name updated to - isPangramUsingSet(String s)

* Updated the testcases PangramTest.java

Successfully updated the testcases in this same PR branch

---------

Co-authored-by: Debasish Biswas <debasishbsws.dev@gmail.com>

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

@@ -1,5 +1,7 @@
 package com.thealgorithms.strings;
 
+import java.util.HashSet;
+
 /**
  * Wikipedia: https://en.wikipedia.org/wiki/Pangram
  */
@@ -15,6 +17,22 @@ public class Pangram {
         assert !isPangram("\u0000/\\");
     }
 
+    /**
+     * Checks if a String is considered a Pangram
+     *
+     * @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<Character>();
+        s = s.trim().toLowerCase();
+        for (int i = 0; i < s.length(); i++)
+            if (s.charAt(i) != ' ') alpha.add(s.charAt(i));
+        if (alpha.size() == 26) return true;
+        return false;
+    }
+
     /**
      * Checks if a String is considered a Pangram
      *

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

@@ -17,5 +17,10 @@ public class PangramTest {
         assertFalse(Pangram.isPangram2("The quick brown fox jumps over the azy dog")); // L is missing
         assertFalse(Pangram.isPangram2("+-1234 This string is not alphabetical"));
         assertFalse(Pangram.isPangram2("\u0000/\\ Invalid characters are alright too"));
+
+        assertTrue(Pangram.isPangramUsingSet("The quick brown fox jumps over the lazy dog"));
+        assertFalse(Pangram.isPangramUsingSet("The quick brown fox jumps over the azy dog")); // L is missing
+        assertFalse(Pangram.isPangramUsingSet("+-1234 This string is not alphabetical"));
+        assertFalse(Pangram.isPangramUsingSet("\u0000/\\ Invalid characters are alright too"));
     }
 }