Submission #695274

#	Time	Username	Problem	Language	Result	Execution time	Memory
695274		finn__	Flight to the Ford (BOI22_communication)	C++17	0 / 100	447 ms	200 KiB

communication

#include <bits/stdc++.h>
#include "communication.h"
using namespace std;

// 0 -> 0000, 1 -> 0110, 2 -> 1001, 3 -> 1111
int e[4] = {0, 6, 9, 15};
// The inverse of e including errors.
pair<int, int> d[16] = {{0, 2},  // 0000
                        {0, 2},  // 0001
                        {0, 1},  // 0010
                        {1, 2},  // 0011
                        {0, 1},  // 0100
                        {0, 3},  // 0101
                        {1, 3},  // 0110
                        {1, 3},  // 0111
                        {0, 2},  // 1000
                        {0, 2},  // 1001
                        {0, 3},  // 1010
                        {2, 3},  // 1011
                        {1, 2},  // 1100
                        {2, 3},  // 1101
                        {1, 3},  // 1110
                        {1, 3}}; // 1111

int bit_reverse(int N, int X)
{
    int Y = 0;
    for (unsigned i = 0; i < N; i++)
        Y |= ((X >> i) & 1) << (N - i - 1);
    return Y;
}

void encode(int N, int X) // Send exactly 120 bits to encode any message.
{
    X = bit_reverse(30, X - 1);
    for (unsigned i = 0; i < 30; i++)
    {
        int Y = e[X & 3], Z = 0;
        for (unsigned j = 0; j < 4; j++)
            Z = (Z << 1) | send(Y & 1), Y >>= 1;

        X >>= 2;
        X = (X << 1) | (int)(d[Z].second == Y);
    }
}

pair<int, int> get_interval(pair<int, int> p, pair<int, int> q, int i)
{
    switch (i)
    {
    case 0:
        return {p.first, (p.first + p.second) / 2};
    case 1:
        return {(p.first + p.second) / 2, p.second};
    case 2:
        return {q.first, (q.first + q.second) / 2};
    case 3:
        return {(q.first + q.second) / 2, q.second};
    default:
        assert(0);
    }
}

std::pair<int, int> decode(int N)
{
    pair<int, int> p = {0, 1 << 15}, q = {1 << 15, 1 << 30};
    for (unsigned i = 0; i < 30; i++)
    {
        int Y = 0;
        for (unsigned j = 0; j < 4; j++)
            Y = (Y << 1) | receive();
        Y = bit_reverse(4, Y);

        pair<int, int> r = get_interval(p, q, d[Y].first);
        q = get_interval(p, q, d[Y].second);
        p = r;
    }
    return {p.first + 1, q.first + 1};
}

Compilation message (stderr)

communication.cpp: In function 'int bit_reverse(int, int)':
communication.cpp:28:28: warning: comparison of integer expressions of different signedness: 'unsigned int' and 'int' [-Wsign-compare]
   28 |     for (unsigned i = 0; i < N; i++)
      |                          ~~^~~

• Subtask 1: 0 / 15
• Subtask 2: 0 / 85