Submission #661302

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
661302	2022-11-25T12:27:09 Z	chanhchuong123	Mecho (IOI09_mecho)	C++14	100 / 100	672 ms	6880 KB

mecho

// USACO
#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) {
	return x >= 0 && x < n && y >= 0 && y < n
		&& (field[x][y] == 'G' || field[x][y] == 'M');
}

bool mecho_reached(int mecho_dis, int bees_dis){
	return mecho_dis / s < bees_dis;
}

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;
	int r = n * n;
	while (l <= r) {
		vector<vector<bool>> bees_visited(n, vector<bool>(n));
		vector<vector<bool>> mecho_visited(n, vector<bool>(n));
		vector<vector<int>> bees_time(n, vector<int>(n));
		vector<vector<int>> mecho_time(n, vector<int>(n));
		queue<pair<int, int>> q;
		
		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_reached(mecho_time[x][y] + 1, 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 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_reached(mecho_time[nx][ny], 
				bees_time[nx][ny] - eating_time) && mecho_visited[nx][ny]) {
					reached = true;
				}
		}
		if (reached) {
			l = eating_time + 1;
		} else {
			r = eating_time - 1;
		}
	}

	cout << l - 1 << '\n';
}

Compilation message

mecho.cpp: In function 'int main()':
mecho.cpp:78:31: warning: 'mechoy' may be used uninitialized in this function [-Wmaybe-uninitialized]
   78 |   mecho_visited[mechox][mechoy] = true;
      |                               ^
mecho.cpp:78:23: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
   78 |   mecho_visited[mechox][mechoy] = true;
      |                       ^
mecho.cpp:110:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  110 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:110:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  110 |    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	212 KB	Output is correct
2	Correct	0 ms	212 KB	Output is correct
3	Correct	1 ms	212 KB	Output is correct
4	Correct	0 ms	212 KB	Output is correct
5	Correct	0 ms	212 KB	Output is correct
6	Correct	1 ms	212 KB	Output is correct
7	Correct	534 ms	6512 KB	Output is correct
8	Correct	1 ms	212 KB	Output is correct
9	Correct	1 ms	212 KB	Output is correct
10	Correct	1 ms	212 KB	Output is correct
11	Correct	1 ms	212 KB	Output is correct
12	Correct	2 ms	340 KB	Output is correct
13	Correct	2 ms	340 KB	Output is correct
14	Correct	2 ms	340 KB	Output is correct
15	Correct	1 ms	340 KB	Output is correct
16	Correct	1 ms	212 KB	Output is correct
17	Correct	0 ms	212 KB	Output is correct
18	Correct	1 ms	212 KB	Output is correct
19	Correct	1 ms	340 KB	Output is correct
20	Correct	1 ms	340 KB	Output is correct
21	Correct	1 ms	340 KB	Output is correct
22	Correct	1 ms	340 KB	Output is correct
23	Correct	2 ms	340 KB	Output is correct
24	Correct	1 ms	340 KB	Output is correct
25	Correct	2 ms	340 KB	Output is correct
26	Correct	2 ms	340 KB	Output is correct
27	Correct	2 ms	340 KB	Output is correct
28	Correct	2 ms	340 KB	Output is correct
29	Correct	2 ms	340 KB	Output is correct
30	Correct	2 ms	340 KB	Output is correct
31	Correct	2 ms	340 KB	Output is correct
32	Correct	3 ms	340 KB	Output is correct
33	Correct	41 ms	1548 KB	Output is correct
34	Correct	39 ms	1536 KB	Output is correct
35	Correct	75 ms	1524 KB	Output is correct
36	Correct	54 ms	2028 KB	Output is correct
37	Correct	62 ms	2024 KB	Output is correct
38	Correct	117 ms	1876 KB	Output is correct
39	Correct	63 ms	2284 KB	Output is correct
40	Correct	67 ms	2264 KB	Output is correct
41	Correct	131 ms	2260 KB	Output is correct
42	Correct	100 ms	3096 KB	Output is correct
43	Correct	92 ms	2912 KB	Output is correct
44	Correct	168 ms	2916 KB	Output is correct
45	Correct	112 ms	3380 KB	Output is correct
46	Correct	108 ms	3384 KB	Output is correct
47	Correct	205 ms	3380 KB	Output is correct
48	Correct	123 ms	3908 KB	Output is correct
49	Correct	141 ms	3952 KB	Output is correct
50	Correct	243 ms	3908 KB	Output is correct
51	Correct	156 ms	4476 KB	Output is correct
52	Correct	152 ms	4596 KB	Output is correct
53	Correct	291 ms	4556 KB	Output is correct
54	Correct	186 ms	5072 KB	Output is correct
55	Correct	179 ms	5080 KB	Output is correct
56	Correct	351 ms	5056 KB	Output is correct
57	Correct	199 ms	5772 KB	Output is correct
58	Correct	244 ms	5808 KB	Output is correct
59	Correct	428 ms	5720 KB	Output is correct
60	Correct	230 ms	6412 KB	Output is correct
61	Correct	221 ms	6408 KB	Output is correct
62	Correct	482 ms	6384 KB	Output is correct
63	Correct	522 ms	6468 KB	Output is correct
64	Correct	672 ms	6396 KB	Output is correct
65	Correct	596 ms	6460 KB	Output is correct
66	Correct	557 ms	6388 KB	Output is correct
67	Correct	543 ms	6392 KB	Output is correct
68	Correct	471 ms	6416 KB	Output is correct
69	Correct	502 ms	6420 KB	Output is correct
70	Correct	464 ms	6476 KB	Output is correct
71	Correct	489 ms	6416 KB	Output is correct
72	Correct	472 ms	6412 KB	Output is correct
73	Correct	494 ms	6684 KB	Output is correct
74	Correct	537 ms	6812 KB	Output is correct
75	Correct	600 ms	6880 KB	Output is correct
76	Correct	514 ms	6732 KB	Output is correct
77	Correct	534 ms	6812 KB	Output is correct
78	Correct	522 ms	6780 KB	Output is correct
79	Correct	517 ms	6652 KB	Output is correct
80	Correct	493 ms	6648 KB	Output is correct
81	Correct	481 ms	6772 KB	Output is correct
82	Correct	482 ms	6656 KB	Output is correct
83	Correct	517 ms	6612 KB	Output is correct
84	Correct	508 ms	6672 KB	Output is correct
85	Correct	531 ms	6732 KB	Output is correct
86	Correct	516 ms	6740 KB	Output is correct
87	Correct	509 ms	6736 KB	Output is correct
88	Correct	510 ms	6804 KB	Output is correct
89	Correct	504 ms	6552 KB	Output is correct
90	Correct	509 ms	6604 KB	Output is correct
91	Correct	525 ms	6564 KB	Output is correct
92	Correct	550 ms	6560 KB	Output is correct