Submission #839638

#	Time	Username	Problem	Language	Result	Execution time	Memory
839638		sleepntsheep	Combo (IOI18_combo)	C++17	0 / 100	1 ms	208 KiB

combo

#include "combo.h"
#include <cassert>
#include <string>
#include <vector>
using namespace std;

string guess_sequence(int N)
{
    string ans(2, 0);
    int j = 0, fst = -1, C = 0;
    vector<int> non(N+5, 0);

    for (int i = 0; i < 4; ++i)
    {
        if (i == 3) ans[0] = 'Y', ++j;
        else
        {
            ans[0] = "ABXY"[i];
            ans[1] = i ? 'A': 'B';
            int k = press(ans); ++C;
            if (k == 1) ++j, non[1] |= (i ? 1 : 2);
            if (k == 2) j += 2;
            if (k >= 1) { fst = i; break; }
        }
    }

    /* 3 + (N-2) * 2 + 2 = 5 + 2 N - 4  = 2 N + 1 */

    for (int j = 1; j < N; ++j) non[j] |= (1 << fst);

    int st = -1;
    for (int i = j; i < N - 1;)
    {
        int nxt = i + 1;
        for (int j = 0; j < 4; j++)
        {
            if (non[i] & (1 << j)) continue;
            if (j == 3) ans[i] = 'Y';
            else
            {
                ans.resize(i+2);
                ans[i] = "ABXY"[j];

                int g2i = -1;
                for (int k = 0; k < 4; ++k) if (!(non[i+1] & (1 << k))) { g2i = k; break; }
                g2i = 0;
                ans[i+1] = "ABXY"[g2i];

                int k = press(ans); ++C;
                st = -1;
                if (k == i + 1) non[i+1] |= (1 << g2i);
                if (k == i + 2) { st = 2; nxt = i + 2; }
                if (k >= i + 1) break;
            }
        }
        i = nxt;
    }

    ans.resize(N);
    if (st == -1)
    {
        for (int j = 0; j < 4; j++)
        {
            if (non[N-1] & (1 << j)) continue;
            if (j == 3)
                ans[N-1] = 'Y';
            else
            {
                ans[N-1] = "ABXY"[j];
                int k = press(ans); ++C;
                if (k == N) break;
            }
        }
    }


    return ans;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 95