Codeforces 855B - Marvolo Gaunt's Ring

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int N=1e5+5;
const int INF=0x3f3f3f3f;

int a[N];
int premx[N];
int premn[N];
int sufmx[N];
int sufmn[N];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll n,p,q,r;
    cin>>n>>p>>q>>r;
    for(int i=1;i<=n;i++)cin>>a[i];
    premx[0]=-INF,premn[0]=INF;
    for(int i=1;i<=n;i++)premx[i]=max(premx[i-1],a[i]),premn[i]=min(premn[i-1],a[i]);
    sufmx[n+1]=-INF,sufmn[n+1]=INF;
    for(int i=n;i>=1;i--)sufmx[i]=max(sufmx[i+1],a[i]),sufmn[i]=min(sufmn[i+1],a[i]);
    
    ll ans=-8000000000000000000;
    for(int i=1;i<=n;i++)ans=max(ans,max(p*premx[i],p*premn[i])+q*a[i]+max(r*sufmx[i],r*sufmn[i]));
    cout<<ans<<endl;
    return 0; 
} 

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define mem(a,b) memset(a,b,sizeof(a))

const int N=1e5+5;
const ll _INF=-8e18;
ll dp[3][N];
int a[N];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll p,q,r,n;
    cin>>n>>p>>q>>r;
    for(int i=1;i<=n;i++)cin>>a[i];
    
    dp[0][0]=_INF;
    dp[1][0]=_INF;
    dp[2][0]=_INF;
    for(int i=1;i<=n;i++)
    {
        dp[0][i]=max(dp[0][i-1],p*a[i]);
        dp[1][i]=max(dp[1][i-1],dp[0][i]+q*a[i]);
        dp[2][i]=max(dp[2][i-1],dp[1][i]+r*a[i]);
    }
    cout<<dp[2][n]<<endl;
    return 0;
}