#include <bits/stdc++.h>
using namespace std;
/*
a数组存储读入的每个数
b数组表示每个读入的数出现的次数 
*/
int main()
{
    int n,a[10900],b[110];
    double sum=0;
    cin >> n;
    for(int i=1;i<=n;i++)
    {
        cin >> a[i];
        b[a[i]]++;
        sum += a[i];
    }
    cout << fixed << setprecision(2) << 1.0*sum/n << " ";
    //众数：计数数组的最大数下标 
	int max=0;
    for(int i=1;i<=100;i++)
    {
        if(b[i] > b[max]) max = i;
    }
    //众数： 
    cout << max << " ";
    //中位数 
    sort (a+1,a+n+1);
    if(n%2==1) cout << fixed << setprecision(1) <<a[n/2+1]*1.0;
        else cout << fixed << setprecision(1) <<(a[n/2]+a[n/2+1])/2.0;
 return 0;  
}

太难了，花了我11坤分。

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n,a[10900],b[10900];
    double sum=0;
    cin >> n;
    for(int i=1;i<=n;i++)
    {
        cin >> b[i];
        a[b[i]]++;
        sum+=b[i];
    }
    cout << fixed << setprecision(2) << sum/n << " ";
    int max=0;
    for(int i=1;i<=n;i++)
    {
        if(a[b[i]]>max)
        {
            max=a[b[i]];
        }
    }
    cout << max << " ";
    sort (b+1,b+n+1);
    sum=0;
    for(int i=n;i>=1;i--)
    {
        if(n%2==0)
        {
            if(i==n/2)
            {
                sum=b[i]+b[i+1];
                cout << fixed << setprecision(1) << sum/2;
            }
        }
        else
        {
            if(i==n/2)
            {
                sum=b[i+1];
                cout << fixed << setprecision(1) << sum;
            }
        }
    }
}