DP+Suffix/Prefix Array, O(n)

/**
 *    author:  compounding
 *    created: 2024-12-10 14:46:52
 **/
#include <bits/stdc++.h>
using namespace std;
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
#define NeedForSpeed                  \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL);
#define int long long
#define all(x) (x).begin(), (x).end()
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<pair<int, int>> vpi;
#define f first
#define s second
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
#define endl "\n"
const int mod = 1000000007;
int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
const int N = (int)1e5 + 5;
int a[N], maxleft[N], maxright[N], minleft[N], minright[N];
void solve()
{
    int n, p, q, r;
    cin >> n >> p >> q >> r;
    for (int i = 1; i <= n; i++)
    {
        cin >> a[i];
    }
    minleft[1] = a[1], maxleft[1] = a[1];
    for (int i = 2; i <= n; i++)
    {
        minleft[i] = min(minleft[i - 1], a[i]);
        maxleft[i] = max(maxleft[i - 1], a[i]);
    }
    minright[n] = a[n], maxright[n] = a[n];
    for (int i = n - 1; i >= 1; i--)
    {
        minright[i] = min(minright[i + 1], a[i]);
        maxright[i] = max(maxright[i + 1], a[i]);
    }
    int ans = LLONG_MIN;
    for (int i = 1; i <= n; i++)
    {
        int leftval = (p < 0) ? 1LL * minleft[i] * p : 1LL * maxleft[i] * p;
        int rightval = (r < 0) ? 1LL * minright[i] * r : 1LL * maxright[i] * r;
        ans = max(ans, leftval + 1LL * a[i] * q + rightval);
    }
    cout << ans << endl;
    return;
}

signed main()
{
    NeedForSpeed;
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}