Java Program to Find the Missing Number in an Array

         This is one of the most common Java coding interview questions. In an interview, you may be given an integer array containing numbers from 1 to n, where each number is unique (no duplicates are allowed). You will be asked to write a Java program to find the missing number in the array.

Example

int[] numbers = {1, 3, 5, 4, 2, 8, 7};

Output:

Missing number: 6

MissingNumber.java

package com.sample;

public class MissingNumber {
 
        public static void main(String[] args) {
  
                  int[] numbers = {1,4,2,5,3,6,7,9}; 
                  int totalNumbers = numbers.length + 1;
  
                  System.out.println("Total numbers - "+totalNumbers);
  
                    // first to calculate the sum of total numbers
  
                   int sumOfTotalNumbers = (totalNumbers * (totalNumbers + 1)) / 2;
  
                   // find the sum of given array. 
  
                   int sumOfArrayNumbers = 0;
  
                   for (int i=0; i<numbers.length; i++) {
                            sumOfArrayNumbers = sumOfArrayNumbers + numbers[i];
                   }
  
                   int missingNumber = sumOfTotalNumbers - sumOfArrayNumbers;
  
                   System.out.println("Missing number - "+missingNumber);
         }

}

Output:--
Total numbers - 9
Missing number - 8

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