Java Program to find the Missing Number in an Array

        This is one of the basic java coding interview questions. In interview, they will give an integer array from 1 to n and each number of array can not be duplicate. They will ask to write the java code to find the missing number of an array.

For Example:-

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