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Submission #629667

# Submission time Handle Problem Language Result Execution time Memory
629667 2022-08-14T21:29:27 Z 54skyxenon Mecho (IOI09_mecho) C++17
100 / 100
 625 ms 6788 KB 
// From https://usaco.guide/problems/ioi-2009mecho/solution

#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:79:23: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
   79 |   mecho_visited[mechox][mechoy] = true;
      |                       ^
mecho.cpp:111:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  111 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:111:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  111 |    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 0 ms 212 KB Output is correct
4 Correct 0 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 527 ms 6444 KB Output is correct
8 Correct 0 ms 212 KB Output is correct
9 Correct 0 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 376 KB Output is correct
15 Correct 1 ms 212 KB Output is correct
16 Correct 1 ms 212 KB Output is correct
17 Correct 0 ms 340 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 1 ms 340 KB Output is correct
24 Correct 1 ms 264 KB Output is correct
25 Correct 2 ms 340 KB Output is correct
26 Correct 2 ms 340 KB Output is correct
27 Correct 1 ms 340 KB Output is correct
28 Correct 1 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 39 ms 1540 KB Output is correct
34 Correct 40 ms 1608 KB Output is correct
35 Correct 74 ms 1552 KB Output is correct
36 Correct 58 ms 1884 KB Output is correct
37 Correct 52 ms 1876 KB Output is correct
38 Correct 99 ms 1880 KB Output is correct
39 Correct 79 ms 2236 KB Output is correct
40 Correct 66 ms 2364 KB Output is correct
41 Correct 134 ms 2260 KB Output is correct
42 Correct 87 ms 2932 KB Output is correct
43 Correct 87 ms 2912 KB Output is correct
44 Correct 163 ms 2908 KB Output is correct
45 Correct 113 ms 3372 KB Output is correct
46 Correct 105 ms 3500 KB Output is correct
47 Correct 193 ms 3380 KB Output is correct
48 Correct 126 ms 3940 KB Output is correct
49 Correct 138 ms 4004 KB Output is correct
50 Correct 240 ms 3924 KB Output is correct
51 Correct 148 ms 4472 KB Output is correct
52 Correct 149 ms 4488 KB Output is correct
53 Correct 303 ms 4480 KB Output is correct
54 Correct 181 ms 5080 KB Output is correct
55 Correct 200 ms 5064 KB Output is correct
56 Correct 335 ms 5076 KB Output is correct
57 Correct 206 ms 5720 KB Output is correct
58 Correct 194 ms 5728 KB Output is correct
59 Correct 409 ms 5716 KB Output is correct
60 Correct 232 ms 6388 KB Output is correct
61 Correct 229 ms 6428 KB Output is correct
62 Correct 453 ms 6388 KB Output is correct
63 Correct 518 ms 6388 KB Output is correct
64 Correct 625 ms 6392 KB Output is correct
65 Correct 605 ms 6400 KB Output is correct
66 Correct 596 ms 6436 KB Output is correct
67 Correct 530 ms 6384 KB Output is correct
68 Correct 505 ms 6416 KB Output is correct
69 Correct 540 ms 6420 KB Output is correct
70 Correct 562 ms 6412 KB Output is correct
71 Correct 572 ms 6420 KB Output is correct
72 Correct 481 ms 6420 KB Output is correct
73 Correct 524 ms 6612 KB Output is correct
74 Correct 513 ms 6612 KB Output is correct
75 Correct 581 ms 6788 KB Output is correct
76 Correct 494 ms 6688 KB Output is correct
77 Correct 503 ms 6684 KB Output is correct
78 Correct 499 ms 6660 KB Output is correct
79 Correct 488 ms 6652 KB Output is correct
80 Correct 504 ms 6640 KB Output is correct
81 Correct 490 ms 6664 KB Output is correct
82 Correct 508 ms 6732 KB Output is correct
83 Correct 528 ms 6732 KB Output is correct
84 Correct 528 ms 6616 KB Output is correct
85 Correct 537 ms 6616 KB Output is correct
86 Correct 550 ms 6608 KB Output is correct
87 Correct 513 ms 6732 KB Output is correct
88 Correct 507 ms 6620 KB Output is correct
89 Correct 505 ms 6556 KB Output is correct
90 Correct 497 ms 6560 KB Output is correct
91 Correct 501 ms 6604 KB Output is correct
92 Correct 544 ms 6568 KB Output is correct