mD5DSb - Online C++ Compiler & Debugging Tool

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define fi first
#define se second
#define pb push_back
#define el '\n'
#define task "BDARR27"
const int maxN = 3e5;
const int maxM = 3e3;
const ll oo = 1e18 + 9;
int n, k;
int a[maxN+5];
ll pf[maxN+5];

namespace subtask1
{
    ll dp[maxM+5][maxM+5];
    void solve()
    {
        for(int i=1; i<=n; i++)
            for(int j=1; j<=k; j++) dp[i][j] = -oo;
        for(int i=1; i<=n; i++) dp[i][1] = 1LL * pf[i];


        for(int i=1; i<=n; i++)
        {
            for(int j=2; j<=k; j++)
            {
                for(int p=1; p<i; p++)
                {
                    dp[i][j] = max(dp[i][j], dp[p][j-1] + 1LL*j * (pf[i] - pf[p]));
                }
            }
        }
        cout << dp[n][k];
    }
}

namespace subtask2
{
    bool cmp(ll x, ll y)
    {
        return x > y;
    }

    vector<ll> vec;
    void solve()
    {
        memset(pf, 0, sizeof pf);
        for(int i=n; i>=1; i--) pf[i] = pf[i+1] + a[i];
        for(int i=2; i<=n; i++) vec.push_back(pf[i]);
        sort(vec.begin(), vec.end(), cmp);
        ll ans = pf[1];
        for(int i=0; i<k-1; i++) ans = ans + vec[i];
        cout << ans;
    }
}

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    if(fopen(task".inp","r"))
    {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    cin >> n >> k;
    for(int i=1; i<=n; i++)
    {
        cin >> a[i];
        pf[i] = pf[i-1] + a[i];
    }

    subtask2::solve();
    return 0;
}