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Submission #51596

# Submission time Handle Problem Language Result Execution time Memory
51596 2018-06-19T03:01:32 Z model_code Mecho (IOI09_mecho) C++
100 / 100
 264 ms 6684 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 1000

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 7 ms 5240 KB Output is correct
2 Correct 6 ms 5240 KB Output is correct
3 Correct 6 ms 5400 KB Output is correct
4 Correct 6 ms 5400 KB Output is correct
5 Correct 6 ms 5404 KB Output is correct
6 Correct 6 ms 5404 KB Output is correct
7 Correct 152 ms 6328 KB Output is correct
8 Correct 6 ms 6328 KB Output is correct
9 Correct 6 ms 6328 KB Output is correct
10 Correct 6 ms 6328 KB Output is correct
11 Correct 6 ms 6328 KB Output is correct
12 Correct 6 ms 6328 KB Output is correct
13 Correct 6 ms 6328 KB Output is correct
14 Correct 7 ms 6328 KB Output is correct
15 Correct 6 ms 6328 KB Output is correct
16 Correct 6 ms 6328 KB Output is correct
17 Correct 9 ms 6328 KB Output is correct
18 Correct 7 ms 6328 KB Output is correct
19 Correct 6 ms 6328 KB Output is correct
20 Correct 6 ms 6328 KB Output is correct
21 Correct 6 ms 6328 KB Output is correct
22 Correct 6 ms 6328 KB Output is correct
23 Correct 6 ms 6328 KB Output is correct
24 Correct 7 ms 6328 KB Output is correct
25 Correct 7 ms 6328 KB Output is correct
26 Correct 6 ms 6328 KB Output is correct
27 Correct 7 ms 6328 KB Output is correct
28 Correct 8 ms 6328 KB Output is correct
29 Correct 7 ms 6328 KB Output is correct
30 Correct 7 ms 6328 KB Output is correct
31 Correct 7 ms 6328 KB Output is correct
32 Correct 8 ms 6328 KB Output is correct
33 Correct 16 ms 6328 KB Output is correct
34 Correct 17 ms 6328 KB Output is correct
35 Correct 38 ms 6328 KB Output is correct
36 Correct 18 ms 6328 KB Output is correct
37 Correct 19 ms 6328 KB Output is correct
38 Correct 43 ms 6328 KB Output is correct
39 Correct 23 ms 6328 KB Output is correct
40 Correct 22 ms 6328 KB Output is correct
41 Correct 55 ms 6328 KB Output is correct
42 Correct 26 ms 6328 KB Output is correct
43 Correct 45 ms 6328 KB Output is correct
44 Correct 78 ms 6328 KB Output is correct
45 Correct 30 ms 6328 KB Output is correct
46 Correct 32 ms 6328 KB Output is correct
47 Correct 89 ms 6328 KB Output is correct
48 Correct 37 ms 6328 KB Output is correct
49 Correct 53 ms 6328 KB Output is correct
50 Correct 104 ms 6328 KB Output is correct
51 Correct 41 ms 6328 KB Output is correct
52 Correct 40 ms 6328 KB Output is correct
53 Correct 141 ms 6328 KB Output is correct
54 Correct 48 ms 6328 KB Output is correct
55 Correct 44 ms 6328 KB Output is correct
56 Correct 174 ms 6328 KB Output is correct
57 Correct 54 ms 6328 KB Output is correct
58 Correct 61 ms 6328 KB Output is correct
59 Correct 176 ms 6328 KB Output is correct
60 Correct 61 ms 6328 KB Output is correct
61 Correct 64 ms 6328 KB Output is correct
62 Correct 217 ms 6360 KB Output is correct
63 Correct 154 ms 6396 KB Output is correct
64 Correct 264 ms 6396 KB Output is correct
65 Correct 209 ms 6396 KB Output is correct
66 Correct 192 ms 6420 KB Output is correct
67 Correct 181 ms 6420 KB Output is correct
68 Correct 92 ms 6420 KB Output is correct
69 Correct 100 ms 6420 KB Output is correct
70 Correct 99 ms 6420 KB Output is correct
71 Correct 87 ms 6420 KB Output is correct
72 Correct 84 ms 6420 KB Output is correct
73 Correct 76 ms 6576 KB Output is correct
74 Correct 114 ms 6684 KB Output is correct
75 Correct 124 ms 6684 KB Output is correct
76 Correct 125 ms 6684 KB Output is correct
77 Correct 126 ms 6684 KB Output is correct
78 Correct 127 ms 6684 KB Output is correct
79 Correct 93 ms 6684 KB Output is correct
80 Correct 106 ms 6684 KB Output is correct
81 Correct 123 ms 6684 KB Output is correct
82 Correct 102 ms 6684 KB Output is correct
83 Correct 137 ms 6684 KB Output is correct
84 Correct 123 ms 6684 KB Output is correct
85 Correct 142 ms 6684 KB Output is correct
86 Correct 151 ms 6684 KB Output is correct
87 Correct 153 ms 6684 KB Output is correct
88 Correct 160 ms 6684 KB Output is correct
89 Correct 148 ms 6684 KB Output is correct
90 Correct 139 ms 6684 KB Output is correct
91 Correct 148 ms 6684 KB Output is correct
92 Correct 165 ms 6684 KB Output is correct