Submission #752558

#	Time	Username	Problem	Language	Result	Execution time	Memory
752558		GrindMachine	Hacker (BOI15_hac)	C++17	100 / 100	311 ms	19988 KiB

hac

// Om Namah Shivaya

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x, y) ((x + y - 1) / (y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl

#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep1(i, n) for(int i = 1; i <= n; ++i)
#define rev(i, s, e) for(int i = s; i >= e; --i)
#define trav(i, a) for(auto &i : a)

template<typename T>
void amin(T &a, T b) {
    a = min(a, b);
}

template<typename T>
void amax(T &a, T b) {
    a = max(a, b);
}

#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif

/*

refs:
https://github.com/Raghavan098/CP-Codes/blob/master/Baltic/Baltic%2015-hac.cpp

#of hacks = ceil(n/2)
#of protections = floor(n/2)

once hacker fixes index to hack, then protector can protect any segment of len = n/2 that he wants
idk proof

*/

const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;

void solve(int test_case)
{
    ll n; cin >> n;
    vector<ll> a(n);
    rep(i,n) cin >> a[i];

    ll suma = 0;
    rep(i,n) suma += a[i];

    vector<ll> sum_here(n);

    ll sum = 0;
    rep(i,n/2) sum += a[i];

    rep(l,n){
        ll r = (l+n/2-1)%n;
        if(l){
            sum += a[r];
            sum -= a[l-1];
        }

        sum_here[l] = sum;
    }

    multiset<ll> ms;
    rep(l,n){
        if(l > 0 and (l+n/2-1) < n){
            ms.insert(sum_here[l]);
        }
    }

    ll ans = 0;

    rep(hack,n){
        if(hack){
            ms.erase(ms.find(sum_here[hack]));
            ll addl = (hack-n/2+n) % n;
            ms.insert(sum_here[addl]);
        }

        ll val = suma - *ms.rbegin();
        amax(ans, val);
    }

    cout << ans << endl;
}

int main()
{
    fastio;

    int t = 1;
    // cin >> t;

    rep1(i, t) {
        solve(i);
    }

    return 0;
}

• Subtask 1: 20 / 20
• Subtask 2: 20 / 20
• Subtask 3: 20 / 20
• Subtask 4: 40 / 40