Hi, I was solving this problem a few minutes ago, and the following problem is a subproblem of this one.

Given integer $$$n$$$, and array $$$a$$$ consisting of $$$n - 1$$$ integers, all of them are equal to some value $$$b$$$. Later, some integer $$$c$$$ is chosen, such that $$$c \ne b$$$, and beign inserted to the array $$$a$$$ at random position. By given $$$n$$$ and $$$a$$$ find $$$c$$$.

#include <bits/stdc++.h>

using namespace std;

int a[100001] = {0};

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    cin >> n;
    for(int i = 0; i < n; i++)
        cin >> a[i];
    
    return 0;
}