#include <string>
#include <iostream>
#include <tuple>
using namespace std;
int press(std::string p);
tuple<char, char, char> remove_one(char c) {
if (c == 'A') return make_tuple('B', 'X', 'Y');
if (c == 'B') return make_tuple('A', 'X', 'Y');
if (c == 'X') return make_tuple('A', 'B', 'Y');
return make_tuple('A', 'B', 'X');
}
string guess_sequence(int N) {
string res;
// guess the first letter
{
if (press("AB")) {
res += press("AX") ? 'A' : 'B';
} else {
res += press("AX") ? 'X' : 'Y';
}
}
char A, B, C;
tie(A, B, C) = remove_one(res[0]);
for (int i = 1; i < N - 1; i++) {
string a = res, b = res, c = res, d = res;
a += A, b += A, c += A, d += B;
a += A, b += B, c += C;
string p = a + b + c + d;
if (press(p) == i) {
res += C;
} else if (press(p) == i + 1) {
res += B;
} else {
res += A;
}
}
// guess the last letter
{
string a = res, b = res;
a += A, b += B;
if (press(a + b) == N) {
b.pop_back();
res += press(a + b) == N ? A : B;
} else {
res += C;
}
}
return res;
}
