Missing number in array.cpp

/*
Given an array of size N-1 such that it only contains distinct integers in the range of 1 to N. Find the missing element.

Example 1:

Input:
N = 5
A[] = {1,2,3,5}
Output: 4
Example 2:

Input:
N = 10
A[] = {6,1,2,8,3,4,7,10,5}
Output: 9

Your Task :
You don't need to read input or print anything. Complete the function MissingNumber() that takes array and N as input  parameters and returns the value of the missing number.


Expected Time Complexity: O(N)
Expected Auxiliary Space: O(1)


Constraints:
1 ≤ N ≤ 106
1 ≤ A[i] ≤ 106
*/

#include <bits/stdc++.h>
using namespace std;

// Function to get the missing number
int getMissingNo(int a[], int n)
{

	int total = (n + 1) * (n + 2) / 2;
	for (int i = 0; i < n; i++)
		total -= a[i];
	return total;
}

// Driver Code
int main()
{
	int arr[] = { 1, 2, 4, 5, 6 };
	int n = sizeof(arr) / sizeof(arr[0]);
	int miss = getMissingNo(arr, n);
	cout << miss;
}