Submission #950288

#	Time	Username	Problem	Language	Result	Execution time	Memory
950288		kilkuwu	Combo (IOI18_combo)	C++17	0 / 100	1 ms	596 KiB

combo

#include <bits/stdc++.h>

#ifdef LOCAL
#include <string>

std::string guess_sequence(int N);

int press(std::string p);
#else
#include "combo.h"
#endif

#ifdef LOCAL
#include "template\debug.hpp"
#else
#define dbg(...) ;
#define timer(...) ;
#endif

std::string guess_sequence(int N) {

  // Guessing the first character takes 2 moves

  // Now we got N moves left

  // each move, we have to eliminate 2 possibilities
  // AA, AB, AC, BA, BB, BC, CA, CB, CC // these are the possiblities
  // identify one in 2 moves

  // N = 3
  // do something to init in 4 moves

  // 4 * 3 = 12 possibilities

  // take 2 -> solve for first one -> A 
  
  // there are 9 possibilites: 3 more queries 
  // - AB -> ABB
  //         ABC 
  //         ABD
  // - AC -> ACB
  //         ACC
  //         ACD
  // - AD -> ADB
  //         ADC
  //         ADD
  // ADC is our answer
  // we have to do this in 3 moves -> what can we do?
  // we ask ABBABCACBACC -> ask for 4 
  // 2 -> in here -> we got 4 branch
  // ABBABCACC -> 0 -> remove 6 branch -> 3 branch left
  // -> remain 3 branch 
  // it is the answer -> 3 branch
  // every time we can remove 6 branch 
  // // >= 1 -> not be 2 
  // 1. ABBB
  // 1. ABBC -> here -> 3 -> original
  // 1. ABBD
  // -------
  // 2. ABCB
  // 2. ABCC 
  // 2. ABCD -> 0, 1, 3 -> ok it works -> it is definitely one of the thing up here
  // -------
  // 3. ACCB
  // 3. ACCC
  // 3. ACCD -> original
  // ACC
  std::string S;

  auto find_first_char = [&]() -> char {
    int res = press("AB");
    if (res == 0) {
      res = press("XY");
      if (res == 0) {
        return 'Y';
      } else {
        return 'X';
      }
    } else {
      res = press("A");
      if (res == 0) {
        return 'B';
      } else {
        return 'A';
      }
    }
  };

  std::string char_set = "ABXY";

  char first_char = find_first_char();
  dbg(first_char);
  char_set.erase(std::find(char_set.begin(), char_set.end(), first_char));

  std::vector<std::string> candidates(3, std::string(1, first_char));
  for (int i = 0; i < 3; i++) {
    candidates[i] += char_set[i];
  }

  auto check_type = [&](int p) -> bool {
    for (int i = 1; i < 3; i++) {
      if (candidates[i][p] != candidates[0][p]) {
        if (i == 2) return false;
        // i == 1 
        if (candidates[0][p] == candidates[2][p]) {
          // this guy is fraud
          std::swap(candidates[1], candidates[2]);
        } else {
          // which means cand[0] is fraud
          std::swap(candidates[0], candidates[2]);
        }

        return false;
      }
    }
    return true;
  };

  int matched = 1; // this is the match score

  for (int i = 1; i < N - 1; i++) { // N - 2 queries 
    dbg(i, matched);
    for (int j = 0; j < 3; j++) dbg(candidates[j]);
    if (check_type(i - 1)) {
      std::string qstring;
      qstring += candidates[0] + char_set[0];
      qstring += candidates[0] + char_set[1];
      qstring += candidates[1] + char_set[0];

      int res = press(qstring) - matched;

      if (res == 0) {
        candidates[0] = candidates[2];
        candidates[1] = candidates[2];
        for (int j = 0; j < 3; j++) candidates[j] += char_set[j];
        // this means we match another
        matched++;
      } else if (res == 1) {
        candidates[2] = candidates[1];
        candidates[0] += char_set[2];
        candidates[1] += char_set[1];
        candidates[2] += char_set[2];
        // we didn't match
      } else {
        candidates[2] = candidates[0];
        candidates[0] += char_set[0];
        candidates[1] += char_set[0];
        candidates[2] += char_set[1];
      }
    } else {
      std::string qstring;
      qstring += candidates[1] + char_set[0];
      qstring += candidates[1] + char_set[1];
      qstring += candidates[1] + char_set[2];

      int res = press(qstring) - matched;

      if (res == 0) {
        candidates[0] = candidates[2];
        candidates[1] = candidates[2];
      } else if (res == 1) {
        candidates[1] = candidates[0];
        candidates[2] = candidates[0];
      } else {
        candidates[0] = candidates[1];
        candidates[2] = candidates[1];
      }
      matched += 2;
      for (int j = 0; j < 3; j++) candidates[j] += char_set[j];
    }
  }

  dbg(candidates[0]);
  dbg(candidates[1]);
  dbg(candidates[2]);
  // we can do it with 2 more queries

  for (int j = 0; j < 2; j++) {
    if (press(candidates[j]) == N) return candidates[j];
  }

  return candidates[2];
}

#ifdef LOCAL

#define nl '\n'

#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <string>
#include "combo.h"

namespace {

constexpr int MAX_N = 2000;
constexpr int MAX_NUM_MOVES = 8000;

int N;
std::string S;

int num_moves;

void wrong_answer(const char *MSG) {
  printf("Wrong Answer: %s\n", MSG);
  exit(0);
}

}  // namespace

int press(std::string p) {
  dbg(p);
  if (++num_moves > MAX_NUM_MOVES) {
    wrong_answer("too many moves");
  }
  int len = p.length();
  if (len > 4 * N) {
    wrong_answer("invalid press");
  }
  for (int i = 0; i < len; ++i) {
    if (p[i] != 'A' && p[i] != 'B' && p[i] != 'X' && p[i] != 'Y') {
      wrong_answer("invalid press");
    }
  }
  int coins = 0;
  for (int i = 0, j = 0; i < len; ++i) {
    if (j < N && S[j] == p[i]) {
      ++j;
    } else if (S[0] == p[i]) {
      j = 1;
    } else {
      j = 0;
    }
    coins = std::max(coins, j);
  }
  dbg(coins);
  return coins;
}

int main() {
  char buffer[MAX_N + 1];
  if (scanf("%s", buffer) != 1) {
    fprintf(stderr, "Error while reading input\n");
    exit(1);
  }
  S = buffer;
  N = S.length();

  num_moves = 0;
  std::string answer = guess_sequence(N);
  if (answer != S) {
    wrong_answer("wrong guess");
    exit(0);
  }
  printf("Accepted: %d\n", num_moves);
  return 0;
}

#endif

• Subtask 1: 0 / 5
• Subtask 2: 0 / 95