## Tuesday, May 3, 2022

### Question 11 : Find missing number in the array.

You are given an integer array containing 1 to n but one of the numbers from 1 to n in the array is missing. You need to provide the optimum solution to find the missing number.

The number cannot be repeated in the array.:

``````int[] arr1={7,5,6,1,4,2};
Missing numner : 3

int[] arr2={5,3,1,2};
Missing numner : 4``````

#### Solution:

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).

#### Java program to find missing number in an array:

``````public class MissingNumberMain {

public static void main(String[] args) {

int[] arr1={7,5,6,1,4,2};
System.out.println("Missing number from array arr1: "+missingNumber(arr1));
int[] arr2={5,3,1,2};
System.out.println("Missing number from array arr2: "+missingNumber(arr2));

}

public static int missingNumber(int[] arr)
{
int n=arr.length+1;
int sum=n*(n+1)/2;
int restSum=0;
for (int i = 0; i < arr.length; i++) {
restSum+=arr[i];
}
int missingNumber=sum-restSum;
return missingNumber;
}
}``````

When you run the above program, you will get the below output:

``````Missing number from array arr1: 3
Missing number from array arr2: 4``````