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Submission #489757

# Submission time Handle Problem Language Result Execution time Memory
489757 2021-11-24T12:13:41 Z nehasane Mecho (IOI09_mecho) C++14
100 / 100
 617 ms 8300 KB 
//for an editorial and code in C++, visit my blog - https://nehasane.blogspot.com/2021/11/ioi-2009-mecho.html
#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 800;
vector <string> field(MAX_N);
bool bees_visited[MAX_N][MAX_N], mecho_visited[MAX_N][MAX_N];
//mecho_dis records the time taken for mecho to reach node[x][y].
//bees_dis does the same for the bees
int mecho_dis[MAX_N][MAX_N], bees_dis[MAX_N][MAX_N];
queue <pair <int, int>> q;
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};
int n, s;
bool valid_sq(int x, int y){
    if (x >= 0 && x < n && y >= 0 && y < n && (field[x][y] == 'G' || field[x][y] == 'M'))
        return true;
    return false;
}
int main()
{
    cin >> n >> s;
    for (int i = 0; i < n; i++)
        cin >> field[i];
    vector <pair <int, int>> hives;
    int mechox, mechoy, home_x, home_y;
    //find x and y coordinates for for Mecho, the bees and the cave
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            if (field[i][j] == 'M'){
                mechox = i;
                mechoy = j;
            }else if (field[i][j] == 'H'){
                hives.push_back({i, j});
            }else if (field[i][j] == 'D'){
                home_x = i;
                home_y = j;
            }
        }
    }
    //binary search on waiting time
    int l = 0, r = n*n;
    while (l <= r){
        int eating_time = (l + r) / 2;
        memset(bees_visited, false, sizeof(bees_visited));
        memset(mecho_visited, false, sizeof(mecho_visited));
        memset(bees_dis, 0, sizeof(bees_dis));
        memset(mecho_dis, 0, sizeof(mecho_dis));
        //move bees
        for (auto i : hives){
            q.push({i.first, i.second});
            bees_visited[i.first][i.second] = true;
        }
        while (!q.empty()){
            int x = q.front().first, y = q.front().second;
            q.pop();
            for (int i = 0; i < 4; i++){
                int nx = x + dx[i], ny = y + dy[i];
                if (valid_sq(nx, ny) && !bees_visited[nx][ny]){
                    bees_dis[nx][ny] = bees_dis[x][y] + 1;    
                    q.push({nx, ny});
                    bees_visited[nx][ny] = true;
                }
            }
        }
        //move Mecho
        q.push({mechox, mechoy});
        mecho_visited[mechox][mechoy] = true;
        if (bees_dis[mechox][mechoy] <= eating_time)
            q.pop();
        while (!q.empty()){
            int x = q.front().first, y = q.front().second;
            q.pop();
            for (int i = 0; i < 4; i++){
                int nx = x + dx[i], ny = y + dy[i];
                //check if mecho reaces node[x][y] before the bees
                /*divide the time mecho takes to reach a node by s, since mecho
                  walks s steps at a time.
                  substract the eating time from the time taken for the bees to 
                  reach the node, because that time was used by mecho for eating
                */
                if (valid_sq(nx, ny) && !mecho_visited[nx][ny] && 
                    (mecho_dis[x][y] + 1) / s < bees_dis[nx][ny] - eating_time){
                    mecho_visited[nx][ny] = true;
                    q.push({nx, ny});
                    mecho_dis[nx][ny] = mecho_dis[x][y] + 1;
                }
            }
        }
        //check if mecho reached a surrounding node before the bees
        bool mecho_reached = false;
        for (int i = 0; i < 4; i++){
            int nx = home_x+ dx[i], ny = home_y + dy[i];
            if (valid_sq(nx, ny) && (mecho_dis[nx][ny] / s) < bees_dis[nx][ny] - eating_time
                && mecho_visited[nx][ny])
                mecho_reached = true;
        }
        if (mecho_reached)
            l = eating_time + 1;
        else
            r = eating_time - 1;
        }
    cout << l - 1 << '\n';
}

Compilation message

mecho.cpp: In function 'int main()':
mecho.cpp:68:36: warning: 'mechoy' may be used uninitialized in this function [-Wmaybe-uninitialized]
   68 |         if (bees_dis[mechox][mechoy] <= eating_time)
      |             ~~~~~~~~~~~~~~~~~~~~~~~^
mecho.cpp:68:36: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
mecho.cpp:92:37: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
   92 |             int nx = home_x+ dx[i], ny = home_y + dy[i];
      |                                     ^~
mecho.cpp:92:17: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
   92 |             int nx = home_x+ dx[i], ny = home_y + dy[i];
      |                 ^~

Subtask #1
100.0 / 100.0

# Verdict Execution time Memory Grader output
1 Correct 4 ms 6476 KB Output is correct
2 Correct 5 ms 6476 KB Output is correct
3 Correct 4 ms 6476 KB Output is correct
4 Correct 4 ms 6476 KB Output is correct
5 Correct 4 ms 6476 KB Output is correct
6 Correct 5 ms 6476 KB Output is correct
7 Correct 497 ms 8072 KB Output is correct
8 Correct 4 ms 6476 KB Output is correct
9 Correct 5 ms 6548 KB Output is correct
10 Correct 5 ms 6476 KB Output is correct
11 Correct 5 ms 6476 KB Output is correct
12 Correct 7 ms 6476 KB Output is correct
13 Correct 9 ms 6676 KB Output is correct
14 Correct 7 ms 6604 KB Output is correct
15 Correct 5 ms 6476 KB Output is correct
16 Correct 5 ms 6476 KB Output is correct
17 Correct 5 ms 6476 KB Output is correct
18 Correct 5 ms 6484 KB Output is correct
19 Correct 5 ms 6476 KB Output is correct
20 Correct 5 ms 6476 KB Output is correct
21 Correct 6 ms 6476 KB Output is correct
22 Correct 8 ms 6476 KB Output is correct
23 Correct 6 ms 6592 KB Output is correct
24 Correct 8 ms 6476 KB Output is correct
25 Correct 7 ms 6488 KB Output is correct
26 Correct 7 ms 6588 KB Output is correct
27 Correct 7 ms 6612 KB Output is correct
28 Correct 7 ms 6604 KB Output is correct
29 Correct 7 ms 6604 KB Output is correct
30 Correct 7 ms 6604 KB Output is correct
31 Correct 7 ms 6604 KB Output is correct
32 Correct 8 ms 6524 KB Output is correct
33 Correct 38 ms 6860 KB Output is correct
34 Correct 38 ms 6760 KB Output is correct
35 Correct 79 ms 6860 KB Output is correct
36 Correct 65 ms 6916 KB Output is correct
37 Correct 50 ms 6916 KB Output is correct
38 Correct 101 ms 6852 KB Output is correct
39 Correct 59 ms 6988 KB Output is correct
40 Correct 78 ms 6996 KB Output is correct
41 Correct 183 ms 6988 KB Output is correct
42 Correct 80 ms 7244 KB Output is correct
43 Correct 77 ms 7288 KB Output is correct
44 Correct 155 ms 7296 KB Output is correct
45 Correct 99 ms 7380 KB Output is correct
46 Correct 92 ms 7384 KB Output is correct
47 Correct 197 ms 7388 KB Output is correct
48 Correct 101 ms 7504 KB Output is correct
49 Correct 102 ms 7492 KB Output is correct
50 Correct 231 ms 7504 KB Output is correct
51 Correct 142 ms 7504 KB Output is correct
52 Correct 123 ms 7600 KB Output is correct
53 Correct 274 ms 7604 KB Output is correct
54 Correct 150 ms 7636 KB Output is correct
55 Correct 140 ms 7708 KB Output is correct
56 Correct 297 ms 7716 KB Output is correct
57 Correct 171 ms 7832 KB Output is correct
58 Correct 164 ms 7816 KB Output is correct
59 Correct 384 ms 7840 KB Output is correct
60 Correct 202 ms 7952 KB Output is correct
61 Correct 176 ms 7956 KB Output is correct
62 Correct 390 ms 7960 KB Output is correct
63 Correct 581 ms 7980 KB Output is correct
64 Correct 617 ms 7968 KB Output is correct
65 Correct 542 ms 7896 KB Output is correct
66 Correct 534 ms 7960 KB Output is correct
67 Correct 508 ms 7960 KB Output is correct
68 Correct 476 ms 7988 KB Output is correct
69 Correct 519 ms 7988 KB Output is correct
70 Correct 465 ms 7988 KB Output is correct
71 Correct 523 ms 8012 KB Output is correct
72 Correct 459 ms 8012 KB Output is correct
73 Correct 413 ms 8260 KB Output is correct
74 Correct 511 ms 8264 KB Output is correct
75 Correct 476 ms 8268 KB Output is correct
76 Correct 469 ms 8300 KB Output is correct
77 Correct 525 ms 8268 KB Output is correct
78 Correct 480 ms 8140 KB Output is correct
79 Correct 522 ms 8228 KB Output is correct
80 Correct 466 ms 8224 KB Output is correct
81 Correct 483 ms 8228 KB Output is correct
82 Correct 474 ms 8220 KB Output is correct
83 Correct 592 ms 8132 KB Output is correct
84 Correct 490 ms 8264 KB Output is correct
85 Correct 526 ms 8184 KB Output is correct
86 Correct 478 ms 8140 KB Output is correct
87 Correct 521 ms 8184 KB Output is correct
88 Correct 473 ms 8128 KB Output is correct
89 Correct 514 ms 8140 KB Output is correct
90 Correct 492 ms 8128 KB Output is correct
91 Correct 473 ms 8136 KB Output is correct
92 Correct 531 ms 8248 KB Output is correct