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Submission #707423

# Submission time Handle Problem Language Result Execution time Memory
707423 2023-03-09T01:56:45 Z yejihan Mecho (IOI09_mecho) C++17
100 / 100
 647 ms 7436 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 1 ms 324 KB Output is correct
2 Correct 1 ms 324 KB Output is correct
3 Correct 1 ms 212 KB Output is correct
4 Correct 1 ms 212 KB Output is correct
5 Correct 1 ms 212 KB Output is correct
6 Correct 1 ms 212 KB Output is correct
7 Correct 525 ms 7128 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 340 KB Output is correct
12 Correct 3 ms 340 KB Output is correct
13 Correct 2 ms 340 KB Output is correct
14 Correct 3 ms 324 KB Output is correct
15 Correct 1 ms 340 KB Output is correct
16 Correct 1 ms 340 KB Output is correct
17 Correct 1 ms 320 KB Output is correct
18 Correct 1 ms 340 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 1 ms 340 KB Output is correct
24 Correct 2 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 2 ms 340 KB Output is correct
33 Correct 39 ms 1664 KB Output is correct
34 Correct 39 ms 1644 KB Output is correct
35 Correct 74 ms 1620 KB Output is correct
36 Correct 54 ms 2036 KB Output is correct
37 Correct 53 ms 2020 KB Output is correct
38 Correct 97 ms 2044 KB Output is correct
39 Correct 63 ms 2460 KB Output is correct
40 Correct 67 ms 2472 KB Output is correct
41 Correct 134 ms 2460 KB Output is correct
42 Correct 103 ms 3168 KB Output is correct
43 Correct 83 ms 3160 KB Output is correct
44 Correct 173 ms 3148 KB Output is correct
45 Correct 110 ms 3668 KB Output is correct
46 Correct 103 ms 3844 KB Output is correct
47 Correct 196 ms 3668 KB Output is correct
48 Correct 116 ms 4272 KB Output is correct
49 Correct 133 ms 4268 KB Output is correct
50 Correct 224 ms 4264 KB Output is correct
51 Correct 150 ms 4896 KB Output is correct
52 Correct 177 ms 4872 KB Output is correct
53 Correct 315 ms 4868 KB Output is correct
54 Correct 179 ms 5572 KB Output is correct
55 Correct 171 ms 5552 KB Output is correct
56 Correct 335 ms 5532 KB Output is correct
57 Correct 202 ms 6264 KB Output is correct
58 Correct 205 ms 6280 KB Output is correct
59 Correct 392 ms 6256 KB Output is correct
60 Correct 241 ms 7040 KB Output is correct
61 Correct 260 ms 7016 KB Output is correct
62 Correct 436 ms 7024 KB Output is correct
63 Correct 503 ms 7016 KB Output is correct
64 Correct 647 ms 7124 KB Output is correct
65 Correct 596 ms 7088 KB Output is correct
66 Correct 547 ms 7196 KB Output is correct
67 Correct 541 ms 7016 KB Output is correct
68 Correct 460 ms 7044 KB Output is correct
69 Correct 495 ms 7244 KB Output is correct
70 Correct 455 ms 7044 KB Output is correct
71 Correct 490 ms 7052 KB Output is correct
72 Correct 472 ms 7052 KB Output is correct
73 Correct 464 ms 7244 KB Output is correct
74 Correct 501 ms 7372 KB Output is correct
75 Correct 567 ms 7320 KB Output is correct
76 Correct 505 ms 7324 KB Output is correct
77 Correct 506 ms 7436 KB Output is correct
78 Correct 511 ms 7400 KB Output is correct
79 Correct 472 ms 7356 KB Output is correct
80 Correct 481 ms 7416 KB Output is correct
81 Correct 504 ms 7404 KB Output is correct
82 Correct 481 ms 7252 KB Output is correct
83 Correct 534 ms 7252 KB Output is correct
84 Correct 513 ms 7168 KB Output is correct
85 Correct 559 ms 7364 KB Output is correct
86 Correct 519 ms 7248 KB Output is correct
87 Correct 539 ms 7236 KB Output is correct
88 Correct 528 ms 7316 KB Output is correct
89 Correct 543 ms 7184 KB Output is correct
90 Correct 508 ms 7312 KB Output is correct
91 Correct 522 ms 7176 KB Output is correct
92 Correct 559 ms 7184 KB Output is correct