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Submission #445349

# Submission time Handle Problem Language Result Execution time Memory
445349 2021-07-17T14:40:39 Z 233 Mecho (IOI09_mecho) C++17
100 / 100
 259 ms 22388 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 19892 KB Output is correct
4 Correct 10 ms 19788 KB Output is correct
5 Correct 10 ms 19868 KB Output is correct
6 Correct 10 ms 19788 KB Output is correct
7 Correct 142 ms 22140 KB Output is correct
8 Correct 11 ms 19788 KB Output is correct
9 Correct 10 ms 19788 KB Output is correct
10 Correct 11 ms 19908 KB Output is correct
11 Correct 10 ms 19788 KB Output is correct
12 Correct 10 ms 19916 KB Output is correct
13 Correct 10 ms 19888 KB Output is correct
14 Correct 12 ms 19916 KB Output is correct
15 Correct 11 ms 19892 KB Output is correct
16 Correct 10 ms 19916 KB Output is correct
17 Correct 10 ms 19916 KB Output is correct
18 Correct 10 ms 19916 KB Output is correct
19 Correct 11 ms 19932 KB Output is correct
20 Correct 10 ms 19916 KB Output is correct
21 Correct 11 ms 19916 KB Output is correct
22 Correct 11 ms 19928 KB Output is correct
23 Correct 11 ms 19916 KB Output is correct
24 Correct 11 ms 19916 KB Output is correct
25 Correct 12 ms 19916 KB Output is correct
26 Correct 11 ms 19916 KB Output is correct
27 Correct 11 ms 19916 KB Output is correct
28 Correct 11 ms 20012 KB Output is correct
29 Correct 11 ms 20020 KB Output is correct
30 Correct 11 ms 19944 KB Output is correct
31 Correct 12 ms 19996 KB Output is correct
32 Correct 12 ms 19944 KB Output is correct
33 Correct 20 ms 20672 KB Output is correct
34 Correct 21 ms 20556 KB Output is correct
35 Correct 40 ms 20656 KB Output is correct
36 Correct 23 ms 20816 KB Output is correct
37 Correct 23 ms 20676 KB Output is correct
38 Correct 50 ms 20792 KB Output is correct
39 Correct 28 ms 20928 KB Output is correct
40 Correct 27 ms 20932 KB Output is correct
41 Correct 63 ms 20912 KB Output is correct
42 Correct 30 ms 21052 KB Output is correct
43 Correct 31 ms 21060 KB Output is correct
44 Correct 76 ms 20992 KB Output is correct
45 Correct 34 ms 21168 KB Output is correct
46 Correct 34 ms 21188 KB Output is correct
47 Correct 88 ms 21132 KB Output is correct
48 Correct 38 ms 21308 KB Output is correct
49 Correct 38 ms 21316 KB Output is correct
50 Correct 102 ms 21316 KB Output is correct
51 Correct 43 ms 21500 KB Output is correct
52 Correct 44 ms 21552 KB Output is correct
53 Correct 124 ms 21444 KB Output is correct
54 Correct 48 ms 21660 KB Output is correct
55 Correct 48 ms 21676 KB Output is correct
56 Correct 150 ms 21740 KB Output is correct
57 Correct 54 ms 21824 KB Output is correct
58 Correct 53 ms 21872 KB Output is correct
59 Correct 166 ms 21888 KB Output is correct
60 Correct 59 ms 21956 KB Output is correct
61 Correct 59 ms 21964 KB Output is correct
62 Correct 190 ms 22060 KB Output is correct
63 Correct 152 ms 22060 KB Output is correct
64 Correct 259 ms 22000 KB Output is correct
65 Correct 210 ms 22084 KB Output is correct
66 Correct 170 ms 22008 KB Output is correct
67 Correct 165 ms 21988 KB Output is correct
68 Correct 94 ms 21960 KB Output is correct
69 Correct 94 ms 22020 KB Output is correct
70 Correct 81 ms 22008 KB Output is correct
71 Correct 90 ms 22020 KB Output is correct
72 Correct 77 ms 22064 KB Output is correct
73 Correct 79 ms 22212 KB Output is correct
74 Correct 108 ms 22256 KB Output is correct
75 Correct 130 ms 22388 KB Output is correct
76 Correct 114 ms 22212 KB Output is correct
77 Correct 112 ms 22268 KB Output is correct
78 Correct 129 ms 22212 KB Output is correct
79 Correct 96 ms 22232 KB Output is correct
80 Correct 110 ms 22220 KB Output is correct
81 Correct 119 ms 22228 KB Output is correct
82 Correct 109 ms 22196 KB Output is correct
83 Correct 130 ms 22208 KB Output is correct
84 Correct 122 ms 22268 KB Output is correct
85 Correct 128 ms 22224 KB Output is correct
86 Correct 127 ms 22236 KB Output is correct
87 Correct 125 ms 22236 KB Output is correct
88 Correct 130 ms 22084 KB Output is correct
89 Correct 135 ms 22256 KB Output is correct
90 Correct 135 ms 22112 KB Output is correct
91 Correct 133 ms 22212 KB Output is correct
92 Correct 142 ms 22156 KB Output is correct