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Submission #74404

# Submission time Handle Problem Language Result Execution time Memory
74404 2018-08-31T16:09:41 Z vvv3334 Mecho (IOI09_mecho) C++14
100 / 100
 287 ms 22268 KB 
/**
 * A binary search solution for IOI 2009 problem "mecho"
 *
 * This solution should score 100%
 *
 * Carl Hultquist, [email protected]
 */
#include <string.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 17 ms 19832 KB Output is correct
2 Correct 17 ms 19956 KB Output is correct
3 Correct 17 ms 19956 KB Output is correct
4 Correct 18 ms 20104 KB Output is correct
5 Correct 20 ms 20104 KB Output is correct
6 Correct 18 ms 20108 KB Output is correct
7 Correct 170 ms 21664 KB Output is correct
8 Correct 18 ms 21664 KB Output is correct
9 Correct 19 ms 21664 KB Output is correct
10 Correct 20 ms 21664 KB Output is correct
11 Correct 18 ms 21664 KB Output is correct
12 Correct 20 ms 21664 KB Output is correct
13 Correct 17 ms 21664 KB Output is correct
14 Correct 19 ms 21664 KB Output is correct
15 Correct 18 ms 21664 KB Output is correct
16 Correct 18 ms 21664 KB Output is correct
17 Correct 19 ms 21664 KB Output is correct
18 Correct 20 ms 21664 KB Output is correct
19 Correct 18 ms 21664 KB Output is correct
20 Correct 18 ms 21664 KB Output is correct
21 Correct 19 ms 21664 KB Output is correct
22 Correct 18 ms 21664 KB Output is correct
23 Correct 19 ms 21664 KB Output is correct
24 Correct 18 ms 21664 KB Output is correct
25 Correct 19 ms 21664 KB Output is correct
26 Correct 19 ms 21664 KB Output is correct
27 Correct 18 ms 21664 KB Output is correct
28 Correct 20 ms 21664 KB Output is correct
29 Correct 20 ms 21664 KB Output is correct
30 Correct 19 ms 21664 KB Output is correct
31 Correct 19 ms 21664 KB Output is correct
32 Correct 19 ms 21664 KB Output is correct
33 Correct 29 ms 21664 KB Output is correct
34 Correct 28 ms 21664 KB Output is correct
35 Correct 49 ms 21664 KB Output is correct
36 Correct 32 ms 21664 KB Output is correct
37 Correct 32 ms 21664 KB Output is correct
38 Correct 56 ms 21664 KB Output is correct
39 Correct 36 ms 21664 KB Output is correct
40 Correct 36 ms 21664 KB Output is correct
41 Correct 69 ms 21664 KB Output is correct
42 Correct 40 ms 21664 KB Output is correct
43 Correct 42 ms 21664 KB Output is correct
44 Correct 83 ms 21664 KB Output is correct
45 Correct 50 ms 21664 KB Output is correct
46 Correct 43 ms 21664 KB Output is correct
47 Correct 95 ms 21664 KB Output is correct
48 Correct 48 ms 21664 KB Output is correct
49 Correct 47 ms 21664 KB Output is correct
50 Correct 109 ms 21664 KB Output is correct
51 Correct 52 ms 21664 KB Output is correct
52 Correct 51 ms 21664 KB Output is correct
53 Correct 123 ms 21664 KB Output is correct
54 Correct 63 ms 21664 KB Output is correct
55 Correct 59 ms 21664 KB Output is correct
56 Correct 163 ms 21664 KB Output is correct
57 Correct 66 ms 21664 KB Output is correct
58 Correct 77 ms 21664 KB Output is correct
59 Correct 194 ms 21708 KB Output is correct
60 Correct 78 ms 21708 KB Output is correct
61 Correct 108 ms 21756 KB Output is correct
62 Correct 211 ms 21756 KB Output is correct
63 Correct 161 ms 21756 KB Output is correct
64 Correct 287 ms 21756 KB Output is correct
65 Correct 222 ms 21756 KB Output is correct
66 Correct 194 ms 21756 KB Output is correct
67 Correct 177 ms 21764 KB Output is correct
68 Correct 104 ms 21764 KB Output is correct
69 Correct 127 ms 21888 KB Output is correct
70 Correct 89 ms 21888 KB Output is correct
71 Correct 97 ms 21888 KB Output is correct
72 Correct 87 ms 21888 KB Output is correct
73 Correct 94 ms 21944 KB Output is correct
74 Correct 143 ms 22004 KB Output is correct
75 Correct 135 ms 22012 KB Output is correct
76 Correct 128 ms 22012 KB Output is correct
77 Correct 140 ms 22268 KB Output is correct
78 Correct 144 ms 22268 KB Output is correct
79 Correct 110 ms 22268 KB Output is correct
80 Correct 153 ms 22268 KB Output is correct
81 Correct 136 ms 22268 KB Output is correct
82 Correct 122 ms 22268 KB Output is correct
83 Correct 148 ms 22268 KB Output is correct
84 Correct 136 ms 22268 KB Output is correct
85 Correct 146 ms 22268 KB Output is correct
86 Correct 145 ms 22268 KB Output is correct
87 Correct 140 ms 22268 KB Output is correct
88 Correct 174 ms 22268 KB Output is correct
89 Correct 152 ms 22268 KB Output is correct
90 Correct 156 ms 22268 KB Output is correct
91 Correct 156 ms 22268 KB Output is correct
92 Correct 161 ms 22268 KB Output is correct