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Submission #1037043

# Submission time Handle Problem Language Result Execution time Memory
1037043 2024-07-27T23:37:00 Z hippo123 Mecho (IOI09_mecho) C++17
100 / 100
 468 ms 7016 KB 
#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:74:23: 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 0 ms 348 KB Output is correct
2 Correct 1 ms 348 KB Output is correct
3 Correct 0 ms 348 KB Output is correct
4 Correct 0 ms 348 KB Output is correct
5 Correct 0 ms 348 KB Output is correct
6 Correct 0 ms 348 KB Output is correct
7 Correct 349 ms 6620 KB Output is correct
8 Correct 1 ms 344 KB Output is correct
9 Correct 0 ms 344 KB Output is correct
10 Correct 0 ms 360 KB Output is correct
11 Correct 0 ms 348 KB Output is correct
12 Correct 1 ms 348 KB Output is correct
13 Correct 1 ms 348 KB Output is correct
14 Correct 2 ms 348 KB Output is correct
15 Correct 0 ms 348 KB Output is correct
16 Correct 0 ms 348 KB Output is correct
17 Correct 0 ms 344 KB Output is correct
18 Correct 1 ms 344 KB Output is correct
19 Correct 1 ms 348 KB Output is correct
20 Correct 0 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 500 KB Output is correct
26 Correct 1 ms 348 KB Output is correct
27 Correct 1 ms 348 KB Output is correct
28 Correct 1 ms 344 KB Output is correct
29 Correct 1 ms 344 KB Output is correct
30 Correct 1 ms 348 KB Output is correct
31 Correct 1 ms 348 KB Output is correct
32 Correct 1 ms 348 KB Output is correct
33 Correct 28 ms 1680 KB Output is correct
34 Correct 27 ms 1640 KB Output is correct
35 Correct 47 ms 1624 KB Output is correct
36 Correct 36 ms 1936 KB Output is correct
37 Correct 36 ms 2008 KB Output is correct
38 Correct 59 ms 1880 KB Output is correct
39 Correct 43 ms 2356 KB Output is correct
40 Correct 44 ms 2392 KB Output is correct
41 Correct 81 ms 2396 KB Output is correct
42 Correct 61 ms 3068 KB Output is correct
43 Correct 61 ms 3072 KB Output is correct
44 Correct 105 ms 2908 KB Output is correct
45 Correct 76 ms 3532 KB Output is correct
46 Correct 68 ms 3516 KB Output is correct
47 Correct 117 ms 3420 KB Output is correct
48 Correct 90 ms 4232 KB Output is correct
49 Correct 89 ms 4048 KB Output is correct
50 Correct 132 ms 4040 KB Output is correct
51 Correct 99 ms 4608 KB Output is correct
52 Correct 96 ms 4596 KB Output is correct
53 Correct 190 ms 4588 KB Output is correct
54 Correct 125 ms 5196 KB Output is correct
55 Correct 111 ms 5216 KB Output is correct
56 Correct 220 ms 5188 KB Output is correct
57 Correct 145 ms 5852 KB Output is correct
58 Correct 127 ms 5856 KB Output is correct
59 Correct 255 ms 5832 KB Output is correct
60 Correct 166 ms 6528 KB Output is correct
61 Correct 144 ms 6560 KB Output is correct
62 Correct 259 ms 6488 KB Output is correct
63 Correct 346 ms 6520 KB Output is correct
64 Correct 468 ms 6520 KB Output is correct
65 Correct 395 ms 6492 KB Output is correct
66 Correct 388 ms 6512 KB Output is correct
67 Correct 353 ms 6492 KB Output is correct
68 Correct 353 ms 6548 KB Output is correct
69 Correct 340 ms 6492 KB Output is correct
70 Correct 340 ms 6552 KB Output is correct
71 Correct 352 ms 6492 KB Output is correct
72 Correct 299 ms 6548 KB Output is correct
73 Correct 289 ms 6600 KB Output is correct
74 Correct 319 ms 6744 KB Output is correct
75 Correct 334 ms 7016 KB Output is correct
76 Correct 302 ms 6744 KB Output is correct
77 Correct 326 ms 6816 KB Output is correct
78 Correct 294 ms 6788 KB Output is correct
79 Correct 280 ms 6748 KB Output is correct
80 Correct 296 ms 6744 KB Output is correct
81 Correct 318 ms 6748 KB Output is correct
82 Correct 303 ms 6748 KB Output is correct
83 Correct 363 ms 6996 KB Output is correct
84 Correct 294 ms 6744 KB Output is correct
85 Correct 318 ms 6744 KB Output is correct
86 Correct 313 ms 6748 KB Output is correct
87 Correct 309 ms 6748 KB Output is correct
88 Correct 313 ms 6488 KB Output is correct
89 Correct 319 ms 6492 KB Output is correct
90 Correct 327 ms 6684 KB Output is correct
91 Correct 323 ms 6708 KB Output is correct
92 Correct 330 ms 6488 KB Output is correct