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Submission #477633

# Submission time Handle Problem Language Result Execution time Memory
477633 2021-10-02T22:54:20 Z urosk Mecho (IOI09_mecho) C++14
100 / 100
 253 ms 22344 KB 
/**
 * A binary search solution for IOI 2009 problem "mecho"
 *
 * This solution should score 100%
 *
 * Carl Hultquist, [email protected]
 */
#include <bits/stdc++.h>
#include <iostream>
#include <string>
#include <cstdlib>
#include <fstream>
#include <vector>
#include <utility>
#include <deque>

using namespace std;

#define MAX_N 2000

int cx[4] = {1, -1, 0, 0};
int cy[4] = {0, 0, 1, -1};

char mainMap[MAX_N][MAX_N];
bool reachable[MAX_N][MAX_N];

// The time that it takes the bees to reach any cell in the map
int beeDistance[MAX_N][MAX_N];

int n, s;
int dx, dy;
int mx, my;

/**
 * Tests if Mecho is able to reach his home after staying with
 * the honey for the given delay time.
 */
bool test(int delay)
{
    // Check if the bees catch Mecho whilst he is still with
    // the honey.
    if (delay * s >= beeDistance[mx][my])
        return false;

    // Initialise data structures -- at the beginning of the search,
    // Mecho has only reached the cell with the honey. Note that it
    // is possible for the bees to catch Mecho at the honey -- but
    // we checked for this case above, and so if we reach this point
    // we know that Mecho is safe with the honey after the given
    // delay.
    memset(reachable, 0, sizeof(reachable));
    deque<pair<int, pair<int, int> > > q;
    q.push_back(make_pair(delay * s, make_pair(mx, my)));
    reachable[mx][my] = true;

    // Now do the main loop to see what other cells Mecho can reach.
    while (!q.empty())
    {
        int distance = q.front().first;
        int x = q.front().second.first;
        int y = q.front().second.second;

        q.pop_front();

        // If Mecho has reached his home, then we are done.
        if (mainMap[x][y] == 'D')
            return true;

        // Check neighbouring cells
        for (int c = 0; c < 4; c++)
        {
            int nx = x + cx[c];
            int ny = y + cy[c];

            // Check that the cell is valid, that it is not a tree, and
            // that Mecho can get here before the bees.
            if (nx < 0 || nx >= n || ny < 0 || ny >= n || mainMap[nx][ny] == 'T' || (distance + 1) >= beeDistance[nx][ny] || reachable[nx][ny])
                continue;

            // All OK, so add it to the queue
            q.push_back(make_pair(distance + 1, make_pair(nx, ny)));
            reachable[nx][ny] = true;
        }
    }

    // If we reach here, then Mecho was unable to reach his home.
    return false;
}
int main(int argc, char **argv)
{
    // Read in the data
    cin >> n >> s;

    deque<pair<int, int> > bq;
    memset(beeDistance, -1, sizeof(beeDistance));

    for (int i = 0; i < n; i++)
    {
        cin >> ws;
        for (int j = 0; j < n; j++)
        {
            cin >> mainMap[i][j];
            if (mainMap[i][j] == 'H')
            {
                bq.push_back(make_pair(i, j));
                beeDistance[i][j] = 0;
            }
            else if (mainMap[i][j] == 'M')
            {
                mx = i;
                my = j;

                // Bees can travel through the location of the honey
                mainMap[i][j] = 'G';
            }
            else if (mainMap[i][j] == 'D')
            {
                dx = i;
                dy = j;
            }
        }
    }

    // Precompute the time that it takes the bees to reach any other
    // cell in the map.
    while (!bq.empty())
    {
        int x = bq.front().first;
        int y = bq.front().second;

        bq.pop_front();

        for (int c = 0; c < 4; c++)
        {
            int nx = x + cx[c];
            int ny = y + cy[c];

            if (nx < 0 || nx >= n || ny < 0 || ny >= n || mainMap[nx][ny] != 'G' || beeDistance[nx][ny] != -1)
                continue;

            beeDistance[nx][ny] = beeDistance[x][y] + s;
            bq.push_back(make_pair(nx, ny));
        }
    }

    // The bees can never enter Mecho's home, so set this to a large
    // sentinel value.
    beeDistance[dx][dy] = n * n * s;

    // Binary search to find the maximum delay time.
    int low = -1, high = 2 * n * n;
    while (high - low > 1)
    {
        int mid = (low + high) >> 1;
        if (test(mid))
            low = mid;
        else
            high = mid;
    }

    cout << low << endl;
    return 0;
}

Subtask #1
100.0 / 100.0

# Verdict Execution time Memory Grader output
1 Correct 10 ms 19792 KB Output is correct
2 Correct 9 ms 19792 KB Output is correct
3 Correct 9 ms 19792 KB Output is correct
4 Correct 8 ms 19792 KB Output is correct
5 Correct 9 ms 19792 KB Output is correct
6 Correct 10 ms 19836 KB Output is correct
7 Correct 126 ms 22116 KB Output is correct
8 Correct 11 ms 19792 KB Output is correct
9 Correct 8 ms 19792 KB Output is correct
10 Correct 9 ms 19792 KB Output is correct
11 Correct 11 ms 19812 KB Output is correct
12 Correct 10 ms 19920 KB Output is correct
13 Correct 9 ms 19940 KB Output is correct
14 Correct 10 ms 19920 KB Output is correct
15 Correct 11 ms 19920 KB Output is correct
16 Correct 9 ms 19920 KB Output is correct
17 Correct 9 ms 19920 KB Output is correct
18 Correct 9 ms 19920 KB Output is correct
19 Correct 9 ms 19920 KB Output is correct
20 Correct 9 ms 19920 KB Output is correct
21 Correct 9 ms 19892 KB Output is correct
22 Correct 10 ms 19960 KB Output is correct
23 Correct 9 ms 19892 KB Output is correct
24 Correct 10 ms 19880 KB Output is correct
25 Correct 9 ms 19920 KB Output is correct
26 Correct 9 ms 19920 KB Output is correct
27 Correct 9 ms 19920 KB Output is correct
28 Correct 10 ms 19920 KB Output is correct
29 Correct 9 ms 19920 KB Output is correct
30 Correct 10 ms 19920 KB Output is correct
31 Correct 10 ms 20036 KB Output is correct
32 Correct 10 ms 20032 KB Output is correct
33 Correct 20 ms 20648 KB Output is correct
34 Correct 23 ms 20600 KB Output is correct
35 Correct 38 ms 20632 KB Output is correct
36 Correct 21 ms 20816 KB Output is correct
37 Correct 24 ms 20720 KB Output is correct
38 Correct 57 ms 20772 KB Output is correct
39 Correct 25 ms 20836 KB Output is correct
40 Correct 24 ms 20896 KB Output is correct
41 Correct 55 ms 20936 KB Output is correct
42 Correct 28 ms 21072 KB Output is correct
43 Correct 30 ms 21072 KB Output is correct
44 Correct 73 ms 21136 KB Output is correct
45 Correct 32 ms 21196 KB Output is correct
46 Correct 31 ms 21124 KB Output is correct
47 Correct 75 ms 21124 KB Output is correct
48 Correct 37 ms 21288 KB Output is correct
49 Correct 35 ms 21304 KB Output is correct
50 Correct 85 ms 21304 KB Output is correct
51 Correct 41 ms 21476 KB Output is correct
52 Correct 40 ms 21448 KB Output is correct
53 Correct 107 ms 21468 KB Output is correct
54 Correct 46 ms 21704 KB Output is correct
55 Correct 45 ms 21628 KB Output is correct
56 Correct 119 ms 21600 KB Output is correct
57 Correct 54 ms 21864 KB Output is correct
58 Correct 58 ms 21876 KB Output is correct
59 Correct 203 ms 21776 KB Output is correct
60 Correct 58 ms 21960 KB Output is correct
61 Correct 55 ms 22040 KB Output is correct
62 Correct 156 ms 21960 KB Output is correct
63 Correct 152 ms 22088 KB Output is correct
64 Correct 253 ms 22060 KB Output is correct
65 Correct 196 ms 22084 KB Output is correct
66 Correct 184 ms 22024 KB Output is correct
67 Correct 169 ms 21960 KB Output is correct
68 Correct 88 ms 22080 KB Output is correct
69 Correct 104 ms 22088 KB Output is correct
70 Correct 76 ms 21960 KB Output is correct
71 Correct 84 ms 22084 KB Output is correct
72 Correct 67 ms 22104 KB Output is correct
73 Correct 68 ms 22312 KB Output is correct
74 Correct 108 ms 22208 KB Output is correct
75 Correct 116 ms 22236 KB Output is correct
76 Correct 100 ms 22320 KB Output is correct
77 Correct 98 ms 22344 KB Output is correct
78 Correct 113 ms 22304 KB Output is correct
79 Correct 98 ms 22216 KB Output is correct
80 Correct 102 ms 22212 KB Output is correct
81 Correct 102 ms 22252 KB Output is correct
82 Correct 97 ms 22344 KB Output is correct
83 Correct 121 ms 22216 KB Output is correct
84 Correct 113 ms 22332 KB Output is correct
85 Correct 121 ms 22272 KB Output is correct
86 Correct 136 ms 22304 KB Output is correct
87 Correct 125 ms 22264 KB Output is correct
88 Correct 113 ms 22180 KB Output is correct
89 Correct 115 ms 22096 KB Output is correct
90 Correct 120 ms 22216 KB Output is correct
91 Correct 128 ms 22216 KB Output is correct
92 Correct 128 ms 22216 KB Output is correct