#include <iostream> #include <algorithm> #include <vector> #include <string> #include <cassert> using namespace std; int press(string p); string guess_sequence(int N) { string str; str.resize(4 * N); char head; for(char symbol : {'A', 'B', 'X', 'Y'}) { std::fill(str.begin(), str.end(), symbol); if(press(str) == 1) { head = symbol; break; } } assert(head != 0); string res; res.resize(N); res.push_back(head); for(int i = 1 ; i < N ; ++i) { str.clear(); for(char symbol : {'A', 'B', 'X', 'Y'}) { str = res; str.push_back(symbol); for(int j = i + 1 ; j < 4 * N ; ++j) { str[j] = head; } if(press(str) == i + 1) { res.push_back(symbol); break; } } } return res; }