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Submission #444944

# Submission time Handle Problem Language Result Execution time Memory
444944 2021-07-16T00:07:34 Z training4usaco Mecho (IOI09_mecho) C++11
100 / 100
 261 ms 22420 KB 
/**
 * A binary search solution for IOI 2009 problem "mecho"
 *
 * This solution should score 100%
 *
 * Carl Hultquist, [email protected]
 */

#include <iostream>
#include <cstring>
#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 19788 KB Output is correct
2 Correct 10 ms 19788 KB Output is correct
3 Correct 10 ms 19788 KB Output is correct
4 Correct 10 ms 19788 KB Output is correct
5 Correct 10 ms 19888 KB Output is correct
6 Correct 10 ms 19880 KB Output is correct
7 Correct 138 ms 22160 KB Output is correct
8 Correct 10 ms 19788 KB Output is correct
9 Correct 10 ms 19788 KB Output is correct
10 Correct 11 ms 19792 KB Output is correct
11 Correct 10 ms 19788 KB Output is correct
12 Correct 11 ms 19952 KB Output is correct
13 Correct 10 ms 19916 KB Output is correct
14 Correct 11 ms 19996 KB Output is correct
15 Correct 11 ms 19788 KB Output is correct
16 Correct 10 ms 19916 KB Output is correct
17 Correct 11 ms 19916 KB Output is correct
18 Correct 11 ms 19884 KB Output is correct
19 Correct 11 ms 19916 KB Output is correct
20 Correct 10 ms 19932 KB Output is correct
21 Correct 10 ms 19888 KB Output is correct
22 Correct 11 ms 19880 KB Output is correct
23 Correct 11 ms 19916 KB Output is correct
24 Correct 11 ms 19892 KB Output is correct
25 Correct 11 ms 19928 KB Output is correct
26 Correct 11 ms 19916 KB Output is correct
27 Correct 12 ms 19916 KB Output is correct
28 Correct 12 ms 19916 KB Output is correct
29 Correct 12 ms 20012 KB Output is correct
30 Correct 11 ms 20016 KB Output is correct
31 Correct 12 ms 20020 KB Output is correct
32 Correct 11 ms 20032 KB Output is correct
33 Correct 21 ms 20608 KB Output is correct
34 Correct 21 ms 20556 KB Output is correct
35 Correct 41 ms 20548 KB Output is correct
36 Correct 23 ms 20740 KB Output is correct
37 Correct 23 ms 20744 KB Output is correct
38 Correct 50 ms 20824 KB Output is correct
39 Correct 27 ms 20876 KB Output is correct
40 Correct 27 ms 20932 KB Output is correct
41 Correct 64 ms 20940 KB Output is correct
42 Correct 30 ms 21060 KB Output is correct
43 Correct 31 ms 21092 KB Output is correct
44 Correct 77 ms 21076 KB Output is correct
45 Correct 34 ms 21188 KB Output is correct
46 Correct 33 ms 21152 KB Output is correct
47 Correct 90 ms 21316 KB Output is correct
48 Correct 38 ms 21284 KB Output is correct
49 Correct 37 ms 21452 KB Output is correct
50 Correct 106 ms 21388 KB Output is correct
51 Correct 42 ms 21440 KB Output is correct
52 Correct 42 ms 21484 KB Output is correct
53 Correct 123 ms 21444 KB Output is correct
54 Correct 50 ms 21700 KB Output is correct
55 Correct 48 ms 21660 KB Output is correct
56 Correct 143 ms 21696 KB Output is correct
57 Correct 54 ms 21828 KB Output is correct
58 Correct 52 ms 21828 KB Output is correct
59 Correct 169 ms 21904 KB Output is correct
60 Correct 58 ms 21956 KB Output is correct
61 Correct 58 ms 21964 KB Output is correct
62 Correct 185 ms 22032 KB Output is correct
63 Correct 153 ms 21956 KB Output is correct
64 Correct 261 ms 22048 KB Output is correct
65 Correct 202 ms 21960 KB Output is correct
66 Correct 169 ms 21980 KB Output is correct
67 Correct 166 ms 22072 KB Output is correct
68 Correct 95 ms 22048 KB Output is correct
69 Correct 90 ms 22084 KB Output is correct
70 Correct 78 ms 21956 KB Output is correct
71 Correct 85 ms 22052 KB Output is correct
72 Correct 77 ms 22076 KB Output is correct
73 Correct 75 ms 22212 KB Output is correct
74 Correct 110 ms 22308 KB Output is correct
75 Correct 123 ms 22252 KB Output is correct
76 Correct 113 ms 22212 KB Output is correct
77 Correct 115 ms 22340 KB Output is correct
78 Correct 129 ms 22420 KB Output is correct
79 Correct 96 ms 22208 KB Output is correct
80 Correct 107 ms 22296 KB Output is correct
81 Correct 117 ms 22216 KB Output is correct
82 Correct 110 ms 22212 KB Output is correct
83 Correct 131 ms 22236 KB Output is correct
84 Correct 119 ms 22192 KB Output is correct
85 Correct 136 ms 22260 KB Output is correct
86 Correct 130 ms 22264 KB Output is correct
87 Correct 127 ms 22212 KB Output is correct
88 Correct 133 ms 22100 KB Output is correct
89 Correct 138 ms 22212 KB Output is correct
90 Correct 137 ms 22212 KB Output is correct
91 Correct 135 ms 22188 KB Output is correct
92 Correct 143 ms 22124 KB Output is correct