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).

Algorithm:

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.

Code:

import java.util.Scanner;
public class MissingNumber 
{
   public static void main(String[] args) 
   {
      Scanner sc = new Scanner(System.in);
      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);
   }
}

Output:

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