Java: Missing letter from an array of increasing letters

Last update on May 09 2025 12:48:04 (UTC/GMT +8 hours)

79. Find missing letter in a sequence of consecutive letters

Write a Java program that returns the missing letter from an array of increasing letters (upper or lower). Assume there will always be one omission from the array.

Sample Data:
{"A", "B", "D", "E"} -> “C”
{"a", "b", "c", "e"} -> “d”
{"p", "r", "s", "t"} -> “q”

Pictorial Presentation:

Sample Solution-1:

Java Code:

// Import necessary Java classes.
import java.util.Scanner;
import java.util.Arrays;

// Define the 'Main' class.
public class Main {
  // Define the main method for running the program.
  public static void main(String[] args) {
    // Initialize an array of strings representing letters.
    // You can use one of these alternative 'str_arra' arrays by uncommenting them.
    // String[] str_arra = {"A", "B", "D", "E"};
    // String[] str_arra = {"a", "b", "c", "e"};
    String[] str_arra = {"p", "r", "s", "t"};
    System.out.printf("Original array of elements:\n" + Arrays.toString(str_arra));

    // Call the 'test' method to find the missing letter in the array.
    String result = test(str_arra);
    System.out.printf("\nMissing letter in the said array: " + result);
  }

  // Define the 'test' method to find the missing letter in the array.
  public static String test(String[] str_arra) {
    // Calculate the expected character code for the missing letter.
    int c = str_arra[0].charAt(0) + 1;
    
    // Iterate through the array and check for the missing letter.
    for (int i = 1; i < str_arra.length; i++, c++) {
      if (str_arra[i].charAt(0) != c) {
        return String.valueOf((char) c);
      }
    }
    
    // Return an empty string if no letter is missing.
    return "";
  }
} 

Sample Output:

Original array of elements:
[p, r, s, t]
Missing letter in the said array: q

Flowchart:

Sample Solution-2:

Java Code:

// Import necessary Java classes.
import java.util.Scanner;
import java.util.Arrays;

// Define the 'Main' class.
public class Main {
  // Define the main method for running the program.
  public static void main(String[] args) {
    // Initialize an array of strings representing letters.
    // You can use one of these alternative 'str_arra' arrays by uncommenting them.
    String[] str_arra = {"A", "B", "D", "E"};
    // String[] str_arra = {"a", "b", "c", "e"};
    // String[] str_arra = {"p", "r", "s", "t"};
    
    // Print the original array of elements.
    System.out.printf("Original array of elements:\n" + Arrays.toString(str_arra));

    // Call the 'test' method to find the missing letter in the array.
    String result = test(str_arra);
    
    // Print the missing letter found in the array.
    System.out.printf("\nMissing letter in the said array: " + result);
  }

  // Define the 'test' method to find the missing letter in the array.
  public static String test(String[] str_arra) {
    // Iterate through the array to find the missing letter.
    for (int i = 0; i < str_arra.length - 1; i++) {
      // Check the difference between adjacent characters.
      if (str_arra[i + 1].charAt(0) - str_arra[i].charAt(0) > 1) {
        // Calculate and return the missing character as a string.
        String result_char = "" + (char)((int)str_arra[i].charAt(0) + 1);
        return result_char;
      }
    }
    
    // Return an empty string if no letter is missing.
    return "";
  }
}

Sample Output:

Original array of elements:
[A, B, D, E]
Missing letter in the said array: C

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to find multiple missing letters from a given sequence of characters.
• Write a Java program to check if a given sequence of characters is in perfect alphabetical order.
• Write a Java program to determine if a given sequence of letters forms a valid consecutive range.
• Write a Java program to find the missing uppercase and lowercase letters in a given character sequence.

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