Pangram checker in java

Carvia Tech | September 12, 2020 | 2 min read | 3,206 views | Java Coding Challenges


Pangram

A pangram is a sentence containing every letter in the English Alphabet (a-z).

Pangram example: The quick brown fox jumps over the lazy dog

Pack my box with five dozen liquor jugs.

— Pangram

Approach:

  1. Create an boolean array that can hold 26 boolean corresponding to each alphabet in English.

  2. Traverse each character of the sentence and mark corresponding index (a=0, b=1,.. z=26) in the boolean array. Take care of upper and lower case.

  3. Traverse through the entire boolean array and see if all characters are covered. If all positions are set to true then input sentence is a pangram.

Pangram Source
public class Pangram {

    public boolean checkPangram(String str) {
        boolean[] mark = new boolean[26];

        int index = 0;
        for (int i = 0; i < str.length(); i++) {
            // If uppercase character, subtract 'A' to find index.
            if ('A' <= str.charAt(i) && str.charAt(i) <= 'Z')
                index = str.charAt(i) - 'A';
            else if ('a' <= str.charAt(i) && str.charAt(i) <= 'z')
                index = str.charAt(i) - 'a';
            mark[index] = true;
        }
        for (int i = 0; i <= 25; i++)
            if (!mark[i])
                return (false);
        return (true);
    }
}

A slightly optimized version of the same program can use an integer (has 32 bits) to hold the state of 26 alphabets by use of Bitwise OR and left shift operator.

Optimized Version
private void pangramEfficient() {
    String s = "The quick brown fox jumps over the lazy dog";
    int i = 0;
    for (char c : s.toCharArray()) {
        int x = Character.toUpperCase(c);
        if (x >= 'A' && x <= 'Z') {
            i |= 1 << (x - 'A');    (1)
        }
    }
    if (i == (1 << (1 + 'Z' - 'A')) - 1) {  (2)
        System.out.println("input is a pangram");
    } else {
        System.out.println("input is not a pangram");
    }
}
1 We are setting nth bit in the integer, where n = 0 for a and n=26 for z. Bitwise ORing can be used to set nth bit of a integer.
2 We are checking if first 26 bits (corresponding to each alphabet) are set or not

No program is complete without a accompanying testcase. Lets write a simple Junit test for Pangram Checker.

Junit Test
import org.junit.Test;

import static org.junit.Assert.assertTrue;

public class PangramTest {
    private Pangram pangramChecker = new Pangram();

    @Test
    public void checkPangram() {
        String str = "The quick brown fox jumps over the lazy dog";
        assertTrue(pangramChecker.checkPangram(str));
    }
}

Thats all.


Java Coding Challenges:
  1. Reverse position of words in a string using recursion
  2. Check if the given string is palindrome
  3. Find two numbers of which the product is maximum in an array
  4. Check a number is Prime: Java Coding Problem
  5. Create anagram buckets from a given input array of words
  6. Anagrams string checker in Java
  7. Reverse a string using recursion in Java
See all articles in Java Coding Challenges
Top articles in this category:
  1. RBS Java Programming Interview Questions
  2. Multi-threading Java Interview Questions for Investment Bank
  3. Citibank Java developer interview questions
  4. BlackRock Java Interview Questions
  5. Morgan Stanley Java Interview Questions
  6. Sapient Global Market Java Interview Questions and Coding Exercise
  7. Goldman Sachs Java Interview Questions

Find more on this topic:

Recommended books for interview preparation:

This website uses cookies to ensure you get the best experience on our website. more info