Java: Find a missing number in an array

Last update on May 09 2025 12:51:43 (UTC/GMT +8 hours)

24. Find missing number in array

Write a Java program to find a missing number in an array.

Pictorial Presentation:

Sample Solution:

Java Code:

// Import the java.util package to use utility classes, including Scanner.
import java.util.*;

// Define a class named Exercise24.
public class Exercise24 {
    // The main method for executing the program.
    public static void main(String[] args) {
        // Declare variables for total number and an array of integers.
        int total_num;
        int[] numbers = new int[]{1, 2, 3, 4, 6, 7};

        // Assign the value 7 to the variable total_num.
        total_num = 7;

        // Calculate the expected sum of numbers using the arithmetic sum formula.
        int expected_num_sum = total_num * ((total_num + 1) / 2);

        // Initialize a variable to store the sum of numbers.
        int num_sum = 0;

        // Iterate through the elements of the 'numbers' array.
        for (int i : numbers) {
            // Add each element to the 'num_sum' variable.
            num_sum += i;
        }

        // Calculate the missing number by subtracting 'num_sum' from 'expected_num_sum'.
        System.out.print(expected_num_sum - num_sum);

        // Print a newline character to end the line.
        System.out.print("\n");
    }
}

Sample Data: 1,2,3,4,6,7

Sample Output:

                                                                              
5

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to find multiple missing numbers in an array of consecutive numbers.
• Write a Java program to find the smallest missing positive integer in an unsorted array.
• Write a Java program to find a missing number in an array that contains duplicates.
• Write a Java program to find a missing number in an arithmetic sequence.

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