#include <string>
#include <vector>
#include <numeric> // Not strictly needed but good practice
// Forward declaration or include header provided by contest environment
// #include "combo.h"
extern int press(std::string p);
std::string guess_sequence(int N) {
std::string guessed_S = "";
std::vector<char> all_chars = {'A', 'B', 'X', 'Y'};
if (N == 0) {
return "";
}
// --- Step 1: Determine the first character S[0] ---
// Try A
if (press("A") == 1) {
guessed_S = "A";
} else if (press("B") == 1) { // Try B if A failed
guessed_S = "B";
} else { // If A and B failed, try X
// If press("X") == 1, it's X. Otherwise, it must be Y.
if (press("X") == 1) {
guessed_S = "X";
} else {
guessed_S = "Y";
}
}
// --- Step 2: Determine the remaining characters S[1] to S[N-1] ---
while (guessed_S.length() < N) {
int k = guessed_S.length();
char next_char = 0; // To store the determined next character
// Try appending 'A', 'B', 'X' one by one.
// If press(current_guess + candidate) returns k+1, we found the next char.
// If A, B, X don't work, the next char must be Y.
if (press(guessed_S + 'A') == k + 1) {
next_char = 'A';
} else if (press(guessed_S + 'B') == k + 1) {
next_char = 'B';
} else if (press(guessed_S + 'X') == k + 1) {
next_char = 'X';
} else {
next_char = 'Y'; // Must be Y if others failed
}
// Append the determined character
// Using push_back might be slightly more efficient than += for single chars
guessed_S.push_back(next_char);
}
return guessed_S;
}
