Pangram Check

/*
 * Problem : Process text.
 * Input   : One line of text.
 * Output  : true or false.
 * Approach: Mark each letter.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static boolean solve(String s) {
        // Step 1: One flag for each letter. seen[0] is for a, seen[1] is for b, and so on.
        boolean[] seen = new boolean[26];
        int count = 0;

        for (int i = 0; i < s.length(); i++) {
            char letter = Character.toLowerCase(s.charAt(i));

            // Step 2: Count each letter the first time we see it.
            if (letter >= 'a' && letter <= 'z' && !seen[letter - 'a']) {
                seen[letter - 'a'] = true;
                count++;
            }
        }

        // Step 3: A pangram has all 26 letters.
        return count == 26;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.hasNextLine() ? scanner.nextLine() : "";
        System.out.println(solve(s));
    }
}