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home / developersection / forums / write a program to find the missing number in an array of integers.
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Revati S Misra
Revati S Misra

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2 Answers

Aryan Kumar
Aryan Kumar 24 Apr 2023
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public class MissingNumber {
   public static void main(String[] args) {
       int[] arr = {1, 2, 3, 4, 6, 7, 8, 9, 10}; // array with missing number
       int n = arr.length + 1; // length of original array
       
       int sum = n * (n + 1) / 2; // sum of integers from 1 to n
       
       for (int i = 0; i < arr.length; i++) {
           sum -= arr[i]; // subtract each element in the array from the sum
       }
       
       System.out.println("The missing number is: " + sum); // output the missing number
   }
}

This program calculates the sum of integers from 1 to n (where n is the length of the original array plus one), and then subtracts each element in the array from the sum. The result is the missing number in the array. In the example array above, the missing number is 5.

Krishnapriya Rajeev
Krishnapriya Rajeev 20 Apr 2023
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The code given below shows how to find the missing number in an array of integers:

class missingNum
{
    public static void main(String[] args)
    {
        int[] nums = { 1, 2, 3, 5, 4, 8, 6};	// Declare and initialize and an integer array.
        int n = nums.length;	// Store length of the integer array
        int sum = ((n + 1) * (n + 2)) / 2;	// Sum of n numbers
        for (int i = 0; i < n; i++)
            sum -= nums[i];		// Subtracts each element from sum
         System.out.println("The missing number is " + sum + ".");
    }
}
OUTPUT:
The missing number is 7.

We can obtain the missing element by subtracting the sum of all elements from the sum of the first n natural numbers, where n is the largest number in the array.

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