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Submission #724718

# Submission time Handle Problem Language Result Execution time Memory
724718 2023-04-15T18:25:17 Z rastervc Mecho (IOI09_mecho) C++17
100 / 100
 218 ms 21716 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 9 ms 19796 KB Output is correct
2 Correct 8 ms 19796 KB Output is correct
3 Correct 7 ms 19796 KB Output is correct
4 Correct 8 ms 19880 KB Output is correct
5 Correct 8 ms 19796 KB Output is correct
6 Correct 8 ms 19796 KB Output is correct
7 Correct 108 ms 21536 KB Output is correct
8 Correct 8 ms 19872 KB Output is correct
9 Correct 9 ms 19848 KB Output is correct
10 Correct 8 ms 19796 KB Output is correct
11 Correct 8 ms 19796 KB Output is correct
12 Correct 9 ms 19924 KB Output is correct
13 Correct 9 ms 19924 KB Output is correct
14 Correct 9 ms 19924 KB Output is correct
15 Correct 9 ms 19824 KB Output is correct
16 Correct 9 ms 19896 KB Output is correct
17 Correct 10 ms 19920 KB Output is correct
18 Correct 11 ms 19864 KB Output is correct
19 Correct 10 ms 19924 KB Output is correct
20 Correct 8 ms 19856 KB Output is correct
21 Correct 10 ms 19924 KB Output is correct
22 Correct 9 ms 19924 KB Output is correct
23 Correct 9 ms 19924 KB Output is correct
24 Correct 9 ms 19924 KB Output is correct
25 Correct 9 ms 19924 KB Output is correct
26 Correct 9 ms 19924 KB Output is correct
27 Correct 11 ms 20004 KB Output is correct
28 Correct 10 ms 19924 KB Output is correct
29 Correct 10 ms 19924 KB Output is correct
30 Correct 10 ms 19932 KB Output is correct
31 Correct 10 ms 19924 KB Output is correct
32 Correct 11 ms 19948 KB Output is correct
33 Correct 19 ms 20564 KB Output is correct
34 Correct 17 ms 20564 KB Output is correct
35 Correct 34 ms 20544 KB Output is correct
36 Correct 20 ms 20564 KB Output is correct
37 Correct 19 ms 20604 KB Output is correct
38 Correct 39 ms 20628 KB Output is correct
39 Correct 22 ms 20684 KB Output is correct
40 Correct 23 ms 20692 KB Output is correct
41 Correct 49 ms 20752 KB Output is correct
42 Correct 25 ms 20804 KB Output is correct
43 Correct 25 ms 20848 KB Output is correct
44 Correct 60 ms 20840 KB Output is correct
45 Correct 29 ms 20884 KB Output is correct
46 Correct 28 ms 20872 KB Output is correct
47 Correct 64 ms 20940 KB Output is correct
48 Correct 32 ms 20988 KB Output is correct
49 Correct 31 ms 20940 KB Output is correct
50 Correct 84 ms 20928 KB Output is correct
51 Correct 36 ms 21068 KB Output is correct
52 Correct 35 ms 21016 KB Output is correct
53 Correct 93 ms 21252 KB Output is correct
54 Correct 41 ms 21176 KB Output is correct
55 Correct 40 ms 21228 KB Output is correct
56 Correct 105 ms 21132 KB Output is correct
57 Correct 50 ms 21232 KB Output is correct
58 Correct 45 ms 21300 KB Output is correct
59 Correct 121 ms 21340 KB Output is correct
60 Correct 48 ms 21380 KB Output is correct
61 Correct 47 ms 21384 KB Output is correct
62 Correct 134 ms 21364 KB Output is correct
63 Correct 133 ms 21428 KB Output is correct
64 Correct 218 ms 21432 KB Output is correct
65 Correct 173 ms 21428 KB Output is correct
66 Correct 144 ms 21432 KB Output is correct
67 Correct 149 ms 21324 KB Output is correct
68 Correct 85 ms 21404 KB Output is correct
69 Correct 92 ms 21388 KB Output is correct
70 Correct 81 ms 21452 KB Output is correct
71 Correct 78 ms 21352 KB Output is correct
72 Correct 63 ms 21340 KB Output is correct
73 Correct 67 ms 21588 KB Output is correct
74 Correct 88 ms 21704 KB Output is correct
75 Correct 119 ms 21708 KB Output is correct
76 Correct 93 ms 21636 KB Output is correct
77 Correct 90 ms 21580 KB Output is correct
78 Correct 102 ms 21608 KB Output is correct
79 Correct 89 ms 21716 KB Output is correct
80 Correct 88 ms 21612 KB Output is correct
81 Correct 100 ms 21592 KB Output is correct
82 Correct 94 ms 21672 KB Output is correct
83 Correct 105 ms 21636 KB Output is correct
84 Correct 99 ms 21620 KB Output is correct
85 Correct 105 ms 21532 KB Output is correct
86 Correct 100 ms 21620 KB Output is correct
87 Correct 99 ms 21644 KB Output is correct
88 Correct 103 ms 21696 KB Output is correct
89 Correct 104 ms 21588 KB Output is correct
90 Correct 118 ms 21624 KB Output is correct
91 Correct 109 ms 21580 KB Output is correct
92 Correct 112 ms 21644 KB Output is correct