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Submission #1088636

# Submission time Handle Problem Language Result Execution time Memory
1088636 2024-09-14T17:29:44 Z v_matei Mecho (IOI09_mecho) C++17
100 / 100
 470 ms 7032 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:132:23: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
  132 |   mecho_visited[mechox][mechoy] = true;
      |                       ^
mecho.cpp:188:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  188 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:188:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  188 |    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 0 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 1 ms 348 KB Output is correct
6 Correct 0 ms 348 KB Output is correct
7 Correct 357 ms 6652 KB Output is correct
8 Correct 1 ms 348 KB Output is correct
9 Correct 0 ms 348 KB Output is correct
10 Correct 1 ms 348 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 1 ms 348 KB Output is correct
15 Correct 0 ms 348 KB Output is correct
16 Correct 0 ms 600 KB Output is correct
17 Correct 0 ms 344 KB Output is correct
18 Correct 1 ms 372 KB Output is correct
19 Correct 0 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 348 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 516 KB Output is correct
29 Correct 1 ms 348 KB Output is correct
30 Correct 1 ms 348 KB Output is correct
31 Correct 2 ms 344 KB Output is correct
32 Correct 2 ms 348 KB Output is correct
33 Correct 29 ms 1732 KB Output is correct
34 Correct 27 ms 1644 KB Output is correct
35 Correct 48 ms 1660 KB Output is correct
36 Correct 37 ms 2008 KB Output is correct
37 Correct 36 ms 2040 KB Output is correct
38 Correct 69 ms 1880 KB Output is correct
39 Correct 47 ms 2356 KB Output is correct
40 Correct 49 ms 2352 KB Output is correct
41 Correct 84 ms 2396 KB Output is correct
42 Correct 62 ms 3068 KB Output is correct
43 Correct 57 ms 3060 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 3520 KB Output is correct
47 Correct 125 ms 3420 KB Output is correct
48 Correct 86 ms 4012 KB Output is correct
49 Correct 82 ms 4108 KB Output is correct
50 Correct 143 ms 3932 KB Output is correct
51 Correct 105 ms 4608 KB Output is correct
52 Correct 97 ms 4844 KB Output is correct
53 Correct 185 ms 4588 KB Output is correct
54 Correct 125 ms 5196 KB Output is correct
55 Correct 124 ms 5260 KB Output is correct
56 Correct 218 ms 5060 KB Output is correct
57 Correct 141 ms 5848 KB Output is correct
58 Correct 135 ms 5864 KB Output is correct
59 Correct 245 ms 5832 KB Output is correct
60 Correct 168 ms 6540 KB Output is correct
61 Correct 152 ms 6536 KB Output is correct
62 Correct 286 ms 6492 KB Output is correct
63 Correct 366 ms 6492 KB Output is correct
64 Correct 470 ms 6516 KB Output is correct
65 Correct 432 ms 6516 KB Output is correct
66 Correct 402 ms 6512 KB Output is correct
67 Correct 381 ms 6492 KB Output is correct
68 Correct 348 ms 6492 KB Output is correct
69 Correct 382 ms 6492 KB Output is correct
70 Correct 339 ms 6492 KB Output is correct
71 Correct 376 ms 6516 KB Output is correct
72 Correct 346 ms 6740 KB Output is correct
73 Correct 297 ms 6748 KB Output is correct
74 Correct 343 ms 6744 KB Output is correct
75 Correct 357 ms 6824 KB Output is correct
76 Correct 326 ms 6812 KB Output is correct
77 Correct 323 ms 6748 KB Output is correct
78 Correct 333 ms 6748 KB Output is correct
79 Correct 317 ms 6780 KB Output is correct
80 Correct 310 ms 6784 KB Output is correct
81 Correct 316 ms 7032 KB Output is correct
82 Correct 309 ms 6784 KB Output is correct
83 Correct 354 ms 6748 KB Output is correct
84 Correct 329 ms 6744 KB Output is correct
85 Correct 352 ms 6744 KB Output is correct
86 Correct 331 ms 6748 KB Output is correct
87 Correct 334 ms 6748 KB Output is correct
88 Correct 338 ms 6492 KB Output is correct
89 Correct 354 ms 6736 KB Output is correct
90 Correct 335 ms 6492 KB Output is correct
91 Correct 351 ms 6936 KB Output is correct
92 Correct 356 ms 6692 KB Output is correct