Submission #1008220

#	Time	Username	Problem	Language	Result	Execution time	Memory
1008220		somefjord	Combo (IOI18_combo)	C++17	100 / 100	33 ms	22884 KiB

combo

#include "combo.h"
#include <bits/stdc++.h>

using namespace std;

char btns[] = {'A', 'B', 'X', 'Y'};

string guess(string known, int n) {
  // cout << known << " " << n << '\n';
  if (known.length() == n)
    return known;

  int x;

  int len = known.length();

  if (!len) {
    x = press("AB");
    if (x == 2) {
      return guess("AB", n);
    } else if (x == 1) {
      x = press("A");
      if (x == 1) {
        return guess("A", n);
      } else {
        return guess("B", n);
      }
    }

    x = press("X");
    if (x == 1) {
      return guess("X", n);
    } else {
      return guess("Y", n);
    }

    // Unreachable
    exit(-1);
  }

  if (len == n - 1) {
    x = press(known + "A" + known + "B");
    if (x == n) {
      x = press(known + "A");
      if (x == n) {
        return known + "A";
      } else {
        return known + "B";
      }
    }

    x = press(known + "X");
    if (x == n) {
      return known + "X";
    } else {
      return known + "Y";
    }
  }

  auto first = known[0];
  char candidates[3];
  {
    int ci = 0;
    for (auto c : btns) {
      if (first == c)
        continue;
      candidates[ci++] = c;
    }
  }

  string q = "";

  q += known;
  q += candidates[0];

  for (auto j = 0; j < 3; ++j) {
    auto candidate2 = candidates[j];

    q += known;
    q += candidates[1];
    q += candidate2;
  }

  x = press(q);
  if (x == len) {
    return guess(known + candidates[2], n);
  } else if (x == len + 1) {
    return guess(known + candidates[0], n);
  } else {
    return guess(known + candidates[1], n);
  }
}

string guess_sequence(int N) { return guess("", N); }

Compilation message (stderr)

combo.cpp: In function 'std::string guess(std::string, int)':
combo.cpp:10:22: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   10 |   if (known.length() == n)
      |       ~~~~~~~~~~~~~~~^~~~

• Subtask 1: 5 / 5
• Subtask 2: 95 / 95