Submission #221104

#	Time	Username	Problem	Language	Result	Execution time	Memory
221104		emil_physmath	The Big Prize (IOI17_prize)	C++17	90 / 100	84 ms	6304 KiB

prize

#include "prize.h"
#include <algorithm>
#include <iostream>
#include <chrono>
#include <random>
#include <vector>
using namespace std;
#ifdef MANSON
mt19937 rng(305);
#else
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#endif // MANSON

namespace
{
    const int maxN = 200000;
    const int mag = 5000;
    int n;

    vector<int> cache[maxN];
    inline vector<int> Ask(int i)
    {
        if (cache[i].size()) return cache[i];
        return cache[i] = ask(i);
    }
    int mx = 0;
    inline bool Cheapest(int i)
    {
        vector<int> res = Ask(i);
        bool f = (res[0] + res[1] >= mx);
        // cerr << i << " is" << (f ? " " : "n't ") << " a cheapy.\n";
        return f;
    }
    int Solve(int l, int r)
    {
        static uniform_int_distribution<int> rnd(1, 2);
        if (rnd(rng) == 2)
        {
            while (l <= r && !Cheapest(l))
            {
                vector<int> res = Ask(l);
                if (res[0] + res[1] == 0) return l;
                ++l;
            }
            if (l > r) return -1;
            int len = 1;
            for (int x = (1 << 17); x >= 1; x >>= 1)
            {
                int R = l + (len + x) - 1;
                if (R > r) continue;
                // if (!Cheapest(R)) continue;
                vector<int> res1 = Ask(l), res2 = Ask(R);
                if (res1[1] == res2[1])
                    len += x;
            }
            if (l + len <= r)
                return Solve(l + len, r);
            return -1;
        }
        while (l <= r && !Cheapest(r))
        {
            vector<int> res = Ask(r);
            if (res[0] + res[1] == 0) return r;
            --r;
        }
        if (l > r) return -1;
        int len = 1;
        for (int x = (1 << 17); x >= 1; x >>= 1)
        {
            int L = r - (len + x) + 1;
            if (L < l) continue;
            if (!Cheapest(L)) continue;
            vector<int> res1 = Ask(L), res2 = Ask(r);
            if (res1[1] == res2[1])
                len += x;
        }
        if (l <= r - len)
            return Solve(l, r - len);
        return -1;
    }
}

int find_best(int n_) {
    n = n_;
    vector<int> p(n);
    iota(p.begin(), p.end(), 0);
    shuffle(p.begin(), p.end(), rng);
    if (p.size() > 446) p.erase(p.begin() + 446, p.end());
    for (int i: p)
    {
        vector<int> res = Ask(i);
        mx = max(mx, res[0] + res[1]);
        if (res[0] + res[1] >= 22)
            break;
        if (res[0] + res[1] == 0) return i;
    }
    vector<int> x;
    for (int i = 0; i * mag < n; ++i)
        x.push_back(i);
    shuffle(x.begin(), x.end(), rng);
    for (int i: x)
    {
        int res = Solve(i * mag, min(i * mag + mag, n - 1));
        if (res != -1)
            return res;
    }
}

Compilation message (stderr)

prize.cpp: In function 'int find_best(int)':
prize.cpp:107:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

• Subtask 1: 20 / 20
• Subtask 2: 70 / 80