Submission #827160

#	Time	Username	Problem	Language	Result	Execution time	Memory
827160		wortelworm	Rice Hub (IOI11_ricehub)	C++17	100 / 100	134 ms	1620 KiB

ricehub

#include "ricehub.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int besthub(int RiceCount, int Length, int RiceFields[], long long Budget)
{
    if (RiceCount <= 5000) {

        ll best_count = 0;
        for (ll i = 0; i < RiceCount; i++)
        {
            ll x = RiceFields[i];

            ll cost = 0;
            ll count = 1;
            ll backwards_index = i-1;
            ll forwards_index = i+1;
            while (cost <= Budget) {
                if (backwards_index < 0 && forwards_index >= RiceCount) {
                    return RiceCount;
                }

                ll backwards = backwards_index < 0 ? 1e9 : x-RiceFields[backwards_index];
                ll forwards = forwards_index >= RiceCount ? 1e9 : RiceFields[forwards_index]-x;

                if (forwards < backwards) {
                    cost += forwards;
                    forwards_index++;
                    count++;
                } else {
                    cost += backwards;
                    backwards_index--;
                    count++;
                }
            }
            count --;
            best_count = max(best_count, count);
        }
        return best_count;
    }


    ll count_before = 0;
    ll count_after = 0;
    ll cost = 0;

    ll best_count = 1;

    for (ll i = 1; i < RiceCount; i++)
    {
        // set the hub at this field
        ll x = RiceFields[i];
        ll distance = RiceFields[i] - RiceFields[i-1];

        // account for the prev_index now also having distance
        count_before++;

        cost += distance * count_before;
        cost -= distance * count_after;

        if (count_after > 0) {
            count_after --;
        }

        auto add_after = [&](){
            while (cost <= Budget && i+count_after < RiceCount-1) {
                count_after++;
                cost += RiceFields[i+count_after] - x;
            }

            if (cost > Budget && count_after > 0) {
                cost -= RiceFields[i+count_after] - x;
                count_after--;
            }
        };


        add_after();
        while (
            count_before > 0
            && (
                cost > Budget
                || (
                    i+count_after < RiceCount-1 &&
                    (x - RiceFields[i-count_before]) >= (RiceFields[i+count_after+1] - x)
                )
            )) {
    
            cost -= x - RiceFields[i-count_before];
            count_before--;

            add_after();
        }

        ll current_count = count_before + count_after + 1;
        if (current_count > best_count) {
            best_count = current_count;
        }
    }

    return best_count;
}

• Subtask 1: 17 / 17
• Subtask 2: 25 / 25
• Subtask 3: 26 / 26
• Subtask 4: 32 / 32