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[] = {1,2,3,4,5,6,7,8,10}
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)

*/

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


class Solution{
  public:
    int MissingNumber(vector<int>& array, int n) {
        // Your code goes here
        int sum=0;
        for(int i=0;i<n-1;i++) sum+=array[i];
        return (n*(n+1)/2)-sum;
    }
};

int main() {
    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;

        vector<int> array(n - 1);
        for (int i = 0; i < n - 1; ++i) cin >> array[i];
        Solution obj;
        cout << obj.MissingNumber(array, n) << "\n";
    }
    return 0;
}