How to find the missing number in a given Array from number 1 to n in Java?

If a single number is missing in an integer array that contains a sequence of numbers values, you can find it basing of the sum of numbers or, basing on the xor of the numbers.

Based on the sum of the numbers −

• The sum of n sequential numbers will be [n*(n+1)]/2. Using this get the sum of the numbers the n numbers.
• Add all the elements in the array.
• Subtract the sum of the numbers in the array from the sum of the n numbers.

Example

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
Output
Enter the n value:
5
Enter (n-1) numbers:
1
2
4
5
Missing number is: 3
Using XOR operation − Another way to find the missing number is using XOR.

• Find the XOR of all the numbers up ton.
• Find the XOR of all the numbers in the array.
• Then find the XOR of both results.

Example

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
Output
Enter the n value:
5
Enter (n-1) numbers:
1
2
4
5
Missing number is: 3