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How to Find Missing Number in a Sorted Array in Java?

Tips to find the missing number in a sorted array:

  1. Find the sum of n number using formula n=n*(n+1)/2

  2. Find the sum of elements present in given array.

  3. Substract (sum of n numbers – sum of elements present in the array).


STEP 1: Start

STEP 2:Declare the array size.

STEP 3:Ask the user to initialize the array size.

STEP 4:Declare the array.

STEP 5:Ask the user to initialize the array elements.

STEP 6:Calculate the sum of first n natural numbers using a formula as sumtotal= n*(n+1)/2

STEP 7: Declare a variable sum to store the sum of array elements.

STEP 8: Using a for loop traverse through each element of the array.

STEP 9: Deduct each element from the total sum calculated.

STEP 10: The remaining element in the sum will be the missing element.

STEP 11: Print the sum.

STEP 12:Stop.


import java.util.Scanner;
public class MissingNumber 
   public static void main(String[] args) 
      Scanner sc = new Scanner(;
      System.out.println("Enter the n value: ");
      int n = sc.nextInt();
      int inpuArray[] = new int[n];
      System.out.println("Enter (n-1) numbers: ");
      for(int i=0; i<=n-2; i++) {
         inpuArray[i] = sc.nextInt();
      //Finding the missing number
      int sumOfAll = (n*(n+1))/2;
      int sumOfArray = 0;
      for(int i=0; i<=n-2; i++) 
         sumOfArray = sumOfArray+inpuArray[i];
      int missingNumber = sumOfAll-sumOfArray;
      System.out.println("Missing number is: "+missingNumber);


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