Submission #491408

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
491408	2021-12-02T01:17:19 Z	nehasane	Mecho (IOI09_mecho)	C++14	100 / 100	633 ms	6804 KB

mecho

#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 800;
vector <string> field(MAX_N);
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;
            }
        }
    }

    int dx[] = {-1, 0, 1, 0};
    int dy[] = {0, -1, 0, 1};

    //  binary search on waiting time
    int l = 0, r = n * n;
    queue <pair <int, int>> q;
    while (l <= r){
        vector <vector <bool>> bees_visited(n, vector<bool>(n, false));
        vector <vector <bool>> mecho_visited(n, vector<bool>(n, false));
        vector <vector <int>> bees_time(n, vector<int>(n, 0));
        vector <vector <int>> mecho_time(n, vector<int>(n, 0));
        
        int eating_time = (l + r) / 2;

        //  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_time[nx][ny] = bees_time[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_time[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_time[x][y] + 1) / s < bees_time[nx][ny] - eating_time){
                        mecho_visited[nx][ny] = true;
                        q.push({nx, ny});
                        mecho_time[nx][ny] = mecho_time[x][y] + 1;
                    }
                }
        }
        
        //  check if mecho reached a node surrounding his cave 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_time[nx][ny] / s) < bees_time[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:70:29: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
   70 |         mecho_visited[mechox][mechoy] = true;
      |                             ^
mecho.cpp:96:37: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
   96 |             int nx = home_x+ dx[i], ny = home_y + dy[i];
      |                                     ^~
mecho.cpp:96:17: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
   96 |             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	0 ms	204 KB	Output is correct
2	Correct	0 ms	204 KB	Output is correct
3	Correct	0 ms	204 KB	Output is correct
4	Correct	1 ms	204 KB	Output is correct
5	Correct	0 ms	204 KB	Output is correct
6	Correct	0 ms	204 KB	Output is correct
7	Correct	578 ms	6496 KB	Output is correct
8	Correct	0 ms	204 KB	Output is correct
9	Correct	0 ms	204 KB	Output is correct
10	Correct	0 ms	204 KB	Output is correct
11	Correct	0 ms	204 KB	Output is correct
12	Correct	1 ms	332 KB	Output is correct
13	Correct	2 ms	332 KB	Output is correct
14	Correct	3 ms	332 KB	Output is correct
15	Correct	0 ms	332 KB	Output is correct
16	Correct	0 ms	328 KB	Output is correct
17	Correct	0 ms	204 KB	Output is correct
18	Correct	1 ms	204 KB	Output is correct
19	Correct	1 ms	332 KB	Output is correct
20	Correct	1 ms	204 KB	Output is correct
21	Correct	2 ms	332 KB	Output is correct
22	Correct	1 ms	332 KB	Output is correct
23	Correct	1 ms	332 KB	Output is correct
24	Correct	1 ms	332 KB	Output is correct
25	Correct	1 ms	332 KB	Output is correct
26	Correct	2 ms	332 KB	Output is correct
27	Correct	1 ms	332 KB	Output is correct
28	Correct	1 ms	332 KB	Output is correct
29	Correct	2 ms	332 KB	Output is correct
30	Correct	2 ms	332 KB	Output is correct
31	Correct	2 ms	332 KB	Output is correct
32	Correct	2 ms	332 KB	Output is correct
33	Correct	39 ms	1528 KB	Output is correct
34	Correct	39 ms	1520 KB	Output is correct
35	Correct	75 ms	1524 KB	Output is correct
36	Correct	56 ms	1876 KB	Output is correct
37	Correct	55 ms	1868 KB	Output is correct
38	Correct	94 ms	1868 KB	Output is correct
39	Correct	64 ms	2232 KB	Output is correct
40	Correct	66 ms	2252 KB	Output is correct
41	Correct	131 ms	2252 KB	Output is correct
42	Correct	85 ms	2920 KB	Output is correct
43	Correct	84 ms	2904 KB	Output is correct
44	Correct	162 ms	2892 KB	Output is correct
45	Correct	117 ms	3368 KB	Output is correct
46	Correct	102 ms	3412 KB	Output is correct
47	Correct	193 ms	3356 KB	Output is correct
48	Correct	128 ms	4056 KB	Output is correct
49	Correct	128 ms	3924 KB	Output is correct
50	Correct	221 ms	3916 KB	Output is correct
51	Correct	154 ms	4628 KB	Output is correct
52	Correct	150 ms	4472 KB	Output is correct
53	Correct	283 ms	4428 KB	Output is correct
54	Correct	182 ms	5176 KB	Output is correct
55	Correct	177 ms	5076 KB	Output is correct
56	Correct	330 ms	4940 KB	Output is correct
57	Correct	204 ms	5704 KB	Output is correct
58	Correct	201 ms	5704 KB	Output is correct
59	Correct	408 ms	5692 KB	Output is correct
60	Correct	244 ms	6500 KB	Output is correct
61	Correct	221 ms	6400 KB	Output is correct
62	Correct	450 ms	6384 KB	Output is correct
63	Correct	523 ms	6468 KB	Output is correct
64	Correct	633 ms	6384 KB	Output is correct
65	Correct	558 ms	6348 KB	Output is correct
66	Correct	522 ms	6312 KB	Output is correct
67	Correct	526 ms	6376 KB	Output is correct
68	Correct	464 ms	6412 KB	Output is correct
69	Correct	485 ms	6420 KB	Output is correct
70	Correct	474 ms	6468 KB	Output is correct
71	Correct	483 ms	6464 KB	Output is correct
72	Correct	467 ms	6408 KB	Output is correct
73	Correct	480 ms	6680 KB	Output is correct
74	Correct	534 ms	6692 KB	Output is correct
75	Correct	547 ms	6804 KB	Output is correct
76	Correct	497 ms	6684 KB	Output is correct
77	Correct	534 ms	6688 KB	Output is correct
78	Correct	508 ms	6644 KB	Output is correct
79	Correct	478 ms	6604 KB	Output is correct
80	Correct	491 ms	6648 KB	Output is correct
81	Correct	492 ms	6648 KB	Output is correct
82	Correct	492 ms	6748 KB	Output is correct
83	Correct	519 ms	6728 KB	Output is correct
84	Correct	559 ms	6604 KB	Output is correct
85	Correct	549 ms	6604 KB	Output is correct
86	Correct	518 ms	6592 KB	Output is correct
87	Correct	518 ms	6620 KB	Output is correct
88	Correct	564 ms	6548 KB	Output is correct
89	Correct	522 ms	6476 KB	Output is correct
90	Correct	510 ms	6692 KB	Output is correct
91	Correct	540 ms	6664 KB	Output is correct
92	Correct	550 ms	6552 KB	Output is correct