Submission #1177548

#	Time	Username	Problem	Language	Result	Execution time	Memory
1177548		madamadam3	Message (IOI24_message)	C++20	81.45 / 100	408 ms	852 KiB

message

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

using namespace std;

using vb = vector<bool>;
using vvb = vector<vb>;

const vb ZERO(31, false);
const vb ONE(31, true);

void trace_vb(vb inp) {
  for (int i = 0; i < (int) inp.size(); i++) {
    cout << (inp[i] ? "1 " : "0 ");
  }
  cout << "\n";
}

void send_message(vb M, vb C) {
  // Stage 1: broadcast the location of the first bit (4 packets)
  int first = 0; while (C[first]) first++;
  for (int i = 0; i < 4; i++) {
    if (first & (1 << i)) send_packet(ONE);
    else send_packet(ZERO);
  }

  // Stage 2: broadcast the information
  M.push_back(true);
  vector<int> mask; for (int i = 0; i < 31; i++) if (!C[i]) mask.push_back(i);
  int S = (int) M.size(), midx = 0;

  int packets = S <= 64 ? 53 : 66;
  for (int i = 0; i < packets; i++) {
    vb packet(31, false);
    if (i < 31) {
      packet[first] = !C[i];
    }

    if (midx < S) {
      int start = i < 31 ? 1 : 0;

      for (int off = start; off < 16 && midx < S; off++) {
        packet[mask[off]] = M[midx++];
      }
    }

    send_packet(packet);
  }
}

vb receive_message(vvb R) {
  vb M;

  // Stage 1: Receive index of first bit
  int first = 0;
  for (int i = 0; i < 4; i++) {
    int ones = 0; for (int bit = 0; bit < 31; bit++) ones += R[i][bit];
    if (ones < 16) continue;

    first |= (1 << i);
  }

  // Stage 2: Determine which bits are safe
  vector<int> safe;
  for (int i = 0; i < 31; i++) {
    if (R[i + 4][first]) safe.push_back(i);
  }


  // Stage 4: Determine message contents
  int packets = (int) R.size() <= 57 ? 53 : 66;
  for (int i = 0; i < packets; i++) {
    int start = i < 31 ? 1 : 0;
    for (int bit = start; bit < 16; bit++) {
      M.push_back(R[4 + i][safe[bit]]);
    }
  }
  
  while (!M.back()) M.pop_back();
  M.pop_back();
  return M;
}

• Subtask 0: 0 / 0
• Subtask 1: 8.1451 / 10
• Subtask 2: 73.3056 / 90