Pangram.java

package com.thealgorithms.strings;

import java.util.HashSet;

/**
 * Wikipedia: https://en.wikipedia.org/wiki/Pangram
 */
public final class Pangram {
 private Pangram() {
 }

 /**
 * Test code
 */
 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/\\");
 }

 /**
 * 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<>();
 s = s.trim().toLowerCase();
 for (int i = 0; i < s.length(); i++) {
 if (s.charAt(i) != ' ') {
 alpha.add(s.charAt(i));
 }
 }
 return alpha.size() == 26;
 }

 /**
 * 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}
 */
 public static boolean isPangram(String s) {
 boolean[] lettersExisting = new boolean[26];
 for (char c : s.toCharArray()) {
 int letterIndex = c - (Character.isUpperCase(c) ? 'A' : 'a');
 if (letterIndex >= 0 && letterIndex < lettersExisting.length) {
 lettersExisting[letterIndex] = true;
 }
 }
 for (boolean letterFlag : lettersExisting) {
 if (!letterFlag) {
 return false;
 }
 }
 return true;
 }

 /**
 * Checks if a String is Pangram or not by checking if each alphabet is present or not
 *
 * @param s The String to check
 * @return {@code true} if s is a Pangram, otherwise {@code false}
 */
 public static boolean isPangram2(String s) {
 if (s.length() < 26) {
 return false;
 }
 s = s.toLowerCase(); // Converting s to Lower-Case
 for (char i = 'a'; i <= 'z'; i++) {
 if (s.indexOf(i) == -1) {
 return false; // if any alphabet is not present, return false
 }
 }
 return true;
 }
}