B. Moamen and k-subarrays

https://codeforces.com/contest/1557/problem/B
#include<bits/stdc++.h>

using namespace std;

const int N = 2e6 + 10;

int a[N];
int n, m;

void solve() {
    cin >> n;
    double sum = 0;
    for (int i = 1; i <= n; i ++) {
        cin >> a[i];
        sum += a[i];
    }   
    sort (a + 1, a + 1 + n);
    printf("%.9lf\n", (sum - a[n]) / (n - 1) + a[n]);
}
int main () {
    int t;
    cin >> t;
    while (t --) solve();
    return 0;
}

通过添加最大数和减少最大数来证明策略是正确的