找到数组中最大的数并扩散至整个数组，整个数组左右两端不受影响
#include <bits/stdc++.h>
usingnamespacestd;
#define ll long long
 
intmain() {
    ll t;
    cin >> t;
    while(t--) {
        ll n;
        cin >> n;
        vector<ll> a(n+1);
        ll x=0;
        for(ll i = 1; i <= n; i++) {
            cin >> a[i];
        }
         for(ll i = 1; i <= n; i++) {
           x=max(x,a[i]);
        }
        cout<<(n-2)*x+a[1]+a[n]<<endl;
    }
 
}