本题只需要去平均值-当前的值$ai$的绝对值最小的数即可

#include <bits/stdc++.h>
using namespace std;
double ans, minn = 9999999;
int main()
{
    int n, a[1005], pos;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
        ans += a[i];
    }
    ans /= n * 1.0;
    for (int i = 1; i <= n; i++)
    {
        if (abs(ans - a[i]) < minn)
        {
            minn = abs(ans - a[i]);
            pos = a[i];
        }
    }
    cout << pos;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    double sum=0;
    int n,a[1005];
    cin >> n;
    for(int i=1;i<=n;i++)
    {
        cin >> a[i];
        sum+=a[i];
    }
    double cha=987996,p;
    int c;
    p=sum/n;
    for(int i=2;i<=n;i++)
    {
        if(p>a[i])
        {
            if(p-a[i]<cha)
            {
                cha=p-a[i];
                c=a[i];
            }
        }
        else
        {
            if(a[i]-p<cha)
            {
                cha=a[i]-p;
                c=a[i];
            }
        }
    }
    cout << c;
}