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Submission #51595

# Submission time Handle Problem Language Result Execution time Memory
51595 2018-06-19T03:01:00 Z model_code Mecho (IOI09_mecho) C++
100 / 100
 287 ms 22148 KB 
/**
 * A binary search solution for IOI 2009 problem "mecho"
 *
 * This solution should score 100%
 *
 * Carl Hultquist, [email protected]
 */

#include <iostream>
#include <string>
#include <cstdlib>
#include <fstream>
#include <vector>
#include <utility>
#include <memory.h>
#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 19 ms 19960 KB Output is correct
2 Correct 17 ms 20072 KB Output is correct
3 Correct 16 ms 20128 KB Output is correct
4 Correct 17 ms 20128 KB Output is correct
5 Correct 16 ms 20128 KB Output is correct
6 Correct 17 ms 20128 KB Output is correct
7 Correct 160 ms 21788 KB Output is correct
8 Correct 16 ms 21788 KB Output is correct
9 Correct 16 ms 21788 KB Output is correct
10 Correct 17 ms 21788 KB Output is correct
11 Correct 20 ms 21788 KB Output is correct
12 Correct 20 ms 21788 KB Output is correct
13 Correct 17 ms 21788 KB Output is correct
14 Correct 20 ms 21788 KB Output is correct
15 Correct 17 ms 21788 KB Output is correct
16 Correct 18 ms 21788 KB Output is correct
17 Correct 17 ms 21788 KB Output is correct
18 Correct 17 ms 21788 KB Output is correct
19 Correct 20 ms 21788 KB Output is correct
20 Correct 18 ms 21788 KB Output is correct
21 Correct 19 ms 21788 KB Output is correct
22 Correct 18 ms 21788 KB Output is correct
23 Correct 18 ms 21788 KB Output is correct
24 Correct 18 ms 21788 KB Output is correct
25 Correct 17 ms 21788 KB Output is correct
26 Correct 20 ms 21788 KB Output is correct
27 Correct 20 ms 21788 KB Output is correct
28 Correct 21 ms 21788 KB Output is correct
29 Correct 19 ms 21788 KB Output is correct
30 Correct 18 ms 21788 KB Output is correct
31 Correct 19 ms 21788 KB Output is correct
32 Correct 20 ms 21788 KB Output is correct
33 Correct 31 ms 21788 KB Output is correct
34 Correct 32 ms 21788 KB Output is correct
35 Correct 55 ms 21788 KB Output is correct
36 Correct 32 ms 21788 KB Output is correct
37 Correct 31 ms 21788 KB Output is correct
38 Correct 77 ms 21788 KB Output is correct
39 Correct 38 ms 21788 KB Output is correct
40 Correct 35 ms 21788 KB Output is correct
41 Correct 74 ms 21788 KB Output is correct
42 Correct 45 ms 21788 KB Output is correct
43 Correct 41 ms 21788 KB Output is correct
44 Correct 92 ms 21788 KB Output is correct
45 Correct 46 ms 21788 KB Output is correct
46 Correct 58 ms 21788 KB Output is correct
47 Correct 102 ms 21788 KB Output is correct
48 Correct 47 ms 21788 KB Output is correct
49 Correct 46 ms 21788 KB Output is correct
50 Correct 121 ms 21788 KB Output is correct
51 Correct 53 ms 21788 KB Output is correct
52 Correct 56 ms 21788 KB Output is correct
53 Correct 149 ms 21788 KB Output is correct
54 Correct 59 ms 21788 KB Output is correct
55 Correct 56 ms 21788 KB Output is correct
56 Correct 213 ms 21788 KB Output is correct
57 Correct 66 ms 21788 KB Output is correct
58 Correct 65 ms 21788 KB Output is correct
59 Correct 195 ms 21788 KB Output is correct
60 Correct 84 ms 21788 KB Output is correct
61 Correct 80 ms 21788 KB Output is correct
62 Correct 213 ms 21788 KB Output is correct
63 Correct 179 ms 21828 KB Output is correct
64 Correct 287 ms 21888 KB Output is correct
65 Correct 272 ms 21888 KB Output is correct
66 Correct 199 ms 21888 KB Output is correct
67 Correct 223 ms 21888 KB Output is correct
68 Correct 117 ms 21888 KB Output is correct
69 Correct 104 ms 21888 KB Output is correct
70 Correct 90 ms 21888 KB Output is correct
71 Correct 92 ms 21888 KB Output is correct
72 Correct 81 ms 21888 KB Output is correct
73 Correct 84 ms 22028 KB Output is correct
74 Correct 185 ms 22028 KB Output is correct
75 Correct 140 ms 22028 KB Output is correct
76 Correct 126 ms 22048 KB Output is correct
77 Correct 153 ms 22112 KB Output is correct
78 Correct 178 ms 22112 KB Output is correct
79 Correct 132 ms 22112 KB Output is correct
80 Correct 129 ms 22112 KB Output is correct
81 Correct 155 ms 22112 KB Output is correct
82 Correct 153 ms 22148 KB Output is correct
83 Correct 172 ms 22148 KB Output is correct
84 Correct 167 ms 22148 KB Output is correct
85 Correct 176 ms 22148 KB Output is correct
86 Correct 164 ms 22148 KB Output is correct
87 Correct 166 ms 22148 KB Output is correct
88 Correct 164 ms 22148 KB Output is correct
89 Correct 176 ms 22148 KB Output is correct
90 Correct 195 ms 22148 KB Output is correct
91 Correct 172 ms 22148 KB Output is correct
92 Correct 179 ms 22148 KB Output is correct