#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);
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 g2 = 0, g2i = -1;
for (int k = 0; k < 4; ++k)
if (!(non[i+1] & (1 << k))) { g2 = "ABXY"[k], g2i = k; break; }
ans[i+1] = g2;
int k = press(ans); ++C;
if (k == i + 1) non[i+1] |= (1 << g2i);
if (k == i + 2) nxt = i + 2;
if (k >= i + 1) break;
}
}
i = nxt;
}
ans.resize(N);
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;
}
}
if (N > 3)
assert(max(N+10,2*N+1)>=C);
return ans;
}
