#include "combo.h" string guess_sequence(int n) { string s, ans; int ret = press("AB"); if (ret == 2) ans += "AB"; else if (ret == 1) { ret = press("A"); if (ret == 1) ans += "A"; else ans += "B"; } else { ret = press("X"); if (ret == 1) ans += "X"; else ans += "Y"; } if (ans.size() == n) return ans; vector<string> vec; if (ans[0] != 'A') vec.pb("A"); if (ans[0] != 'B') vec.pb("B"); if (ans[0] != 'X') vec.pb("X"); if (ans[0] != 'Y') vec.pb("Y"); while (ans.size() + 1 < n) { s = ans + vec[0] + ans + vec[1] + vec[0] + ans + vec[1] + vec[1] + ans + vec[1] + vec[2]; int ret = press(s); if (ret == (int)ans.size()) ans += vec[2]; if (ret == (int)ans.size() + 1) ans += vec[0]; if (ret == (int)ans.size() + 2) ans += vec[1]; } if (press(ans + vec[0]) == n) ans += vec[0]; else if (press(ans + vec[1]) == n) ans += vec[1]; else ans += vec[2]; return ans; }

combo.cpp:3:1: error: 'string' does not name a type; did you mean 'stdin'?
    3 | string guess_sequence(int n) {
      | ^~~~~~
      | stdin