Submission #944913

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
944913	2024-03-13T07:58:15 Z	artixkrishna	Mecho (IOI09_mecho)	C++14	100 / 100	557 ms	7660 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) {
	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:74:31: warning: 'mechoy' may be used uninitialized in this function [-Wmaybe-uninitialized]
   74 |   mecho_visited[mechox][mechoy] = true;
      |                               ^
mecho.cpp:74:23: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
   74 |   mecho_visited[mechox][mechoy] = true;
      |                       ^
mecho.cpp:103:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  103 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:103:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  103 |    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	1 ms	344 KB	Output is correct
2	Correct	1 ms	604 KB	Output is correct
3	Correct	0 ms	348 KB	Output is correct
4	Correct	1 ms	348 KB	Output is correct
5	Correct	0 ms	348 KB	Output is correct
6	Correct	0 ms	604 KB	Output is correct
7	Correct	458 ms	6684 KB	Output is correct
8	Correct	1 ms	344 KB	Output is correct
9	Correct	1 ms	348 KB	Output is correct
10	Correct	1 ms	460 KB	Output is correct
11	Correct	0 ms	344 KB	Output is correct
12	Correct	1 ms	348 KB	Output is correct
13	Correct	2 ms	600 KB	Output is correct
14	Correct	2 ms	452 KB	Output is correct
15	Correct	1 ms	344 KB	Output is correct
16	Correct	1 ms	348 KB	Output is correct
17	Correct	1 ms	812 KB	Output is correct
18	Correct	1 ms	348 KB	Output is correct
19	Correct	1 ms	460 KB	Output is correct
20	Correct	1 ms	348 KB	Output is correct
21	Correct	1 ms	348 KB	Output is correct
22	Correct	1 ms	348 KB	Output is correct
23	Correct	1 ms	348 KB	Output is correct
24	Correct	1 ms	348 KB	Output is correct
25	Correct	1 ms	604 KB	Output is correct
26	Correct	1 ms	348 KB	Output is correct
27	Correct	1 ms	344 KB	Output is correct
28	Correct	2 ms	348 KB	Output is correct
29	Correct	1 ms	348 KB	Output is correct
30	Correct	2 ms	604 KB	Output is correct
31	Correct	2 ms	348 KB	Output is correct
32	Correct	2 ms	348 KB	Output is correct
33	Correct	39 ms	1804 KB	Output is correct
34	Correct	44 ms	1816 KB	Output is correct
35	Correct	67 ms	1628 KB	Output is correct
36	Correct	43 ms	2132 KB	Output is correct
37	Correct	58 ms	2260 KB	Output is correct
38	Correct	79 ms	2088 KB	Output is correct
39	Correct	60 ms	2660 KB	Output is correct
40	Correct	56 ms	2536 KB	Output is correct
41	Correct	124 ms	2536 KB	Output is correct
42	Correct	71 ms	3240 KB	Output is correct
43	Correct	72 ms	3248 KB	Output is correct
44	Correct	141 ms	3164 KB	Output is correct
45	Correct	92 ms	3708 KB	Output is correct
46	Correct	94 ms	3732 KB	Output is correct
47	Correct	170 ms	3728 KB	Output is correct
48	Correct	121 ms	4280 KB	Output is correct
49	Correct	112 ms	4284 KB	Output is correct
50	Correct	213 ms	4592 KB	Output is correct
51	Correct	137 ms	5232 KB	Output is correct
52	Correct	126 ms	4880 KB	Output is correct
53	Correct	267 ms	4908 KB	Output is correct
54	Correct	175 ms	5484 KB	Output is correct
55	Correct	166 ms	5608 KB	Output is correct
56	Correct	299 ms	5720 KB	Output is correct
57	Correct	173 ms	6168 KB	Output is correct
58	Correct	172 ms	6224 KB	Output is correct
59	Correct	337 ms	6192 KB	Output is correct
60	Correct	216 ms	7044 KB	Output is correct
61	Correct	187 ms	7660 KB	Output is correct
62	Correct	354 ms	6932 KB	Output is correct
63	Correct	443 ms	6916 KB	Output is correct
64	Correct	557 ms	6892 KB	Output is correct
65	Correct	494 ms	7056 KB	Output is correct
66	Correct	513 ms	6920 KB	Output is correct
67	Correct	437 ms	7000 KB	Output is correct
68	Correct	413 ms	7396 KB	Output is correct
69	Correct	415 ms	6744 KB	Output is correct
70	Correct	412 ms	6908 KB	Output is correct
71	Correct	460 ms	6800 KB	Output is correct
72	Correct	385 ms	6972 KB	Output is correct
73	Correct	390 ms	7508 KB	Output is correct
74	Correct	429 ms	7224 KB	Output is correct
75	Correct	476 ms	7276 KB	Output is correct
76	Correct	424 ms	7212 KB	Output is correct
77	Correct	428 ms	7260 KB	Output is correct
78	Correct	427 ms	6948 KB	Output is correct
79	Correct	409 ms	7168 KB	Output is correct
80	Correct	395 ms	7148 KB	Output is correct
81	Correct	392 ms	7172 KB	Output is correct
82	Correct	394 ms	7248 KB	Output is correct
83	Correct	418 ms	7164 KB	Output is correct
84	Correct	410 ms	7252 KB	Output is correct
85	Correct	433 ms	7128 KB	Output is correct
86	Correct	410 ms	7000 KB	Output is correct
87	Correct	411 ms	7248 KB	Output is correct
88	Correct	403 ms	7124 KB	Output is correct
89	Correct	422 ms	7080 KB	Output is correct
90	Correct	407 ms	7004 KB	Output is correct
91	Correct	429 ms	7100 KB	Output is correct
92	Correct	449 ms	7128 KB	Output is correct