oj.uz

Submission #646200

# Submission time Handle Problem Language Result Execution time Memory
646200 2022-09-29T06:55:52 Z Pyrodox Mecho (IOI09_mecho) C++17
100 / 100
 620 ms 6764 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:77:23: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
   77 |   mecho_visited[mechox][mechoy] = true;
      |                       ^
mecho.cpp:109:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  109 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:109:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  109 |    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 0 ms 212 KB Output is correct
7 Correct 519 ms 6624 KB Output is correct
8 Correct 1 ms 212 KB Output is correct
9 Correct 1 ms 212 KB Output is correct
10 Correct 0 ms 212 KB Output is correct
11 Correct 0 ms 212 KB Output is correct
12 Correct 1 ms 340 KB Output is correct
13 Correct 2 ms 340 KB Output is correct
14 Correct 3 ms 340 KB Output is correct
15 Correct 0 ms 212 KB Output is correct
16 Correct 0 ms 340 KB Output is correct
17 Correct 1 ms 212 KB Output is correct
18 Correct 1 ms 212 KB Output is correct
19 Correct 1 ms 212 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 340 KB Output is correct
25 Correct 1 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 42 ms 1544 KB Output is correct
34 Correct 39 ms 1724 KB Output is correct
35 Correct 75 ms 1520 KB Output is correct
36 Correct 52 ms 1872 KB Output is correct
37 Correct 54 ms 1876 KB Output is correct
38 Correct 94 ms 1876 KB Output is correct
39 Correct 61 ms 2240 KB Output is correct
40 Correct 64 ms 2272 KB Output is correct
41 Correct 132 ms 2260 KB Output is correct
42 Correct 83 ms 2920 KB Output is correct
43 Correct 84 ms 2912 KB Output is correct
44 Correct 160 ms 2908 KB Output is correct
45 Correct 125 ms 3376 KB Output is correct
46 Correct 103 ms 3384 KB Output is correct
47 Correct 186 ms 3284 KB Output is correct
48 Correct 120 ms 3916 KB Output is correct
49 Correct 128 ms 3908 KB Output is correct
50 Correct 224 ms 3920 KB Output is correct
51 Correct 146 ms 4456 KB Output is correct
52 Correct 143 ms 4460 KB Output is correct
53 Correct 285 ms 4452 KB Output is correct
54 Correct 171 ms 5220 KB Output is correct
55 Correct 171 ms 5112 KB Output is correct
56 Correct 347 ms 5056 KB Output is correct
57 Correct 197 ms 5768 KB Output is correct
58 Correct 199 ms 5708 KB Output is correct
59 Correct 386 ms 5832 KB Output is correct
60 Correct 235 ms 6420 KB Output is correct
61 Correct 218 ms 6400 KB Output is correct
62 Correct 446 ms 6300 KB Output is correct
63 Correct 494 ms 6396 KB Output is correct
64 Correct 620 ms 6356 KB Output is correct
65 Correct 572 ms 6436 KB Output is correct
66 Correct 540 ms 6396 KB Output is correct
67 Correct 514 ms 6456 KB Output is correct
68 Correct 475 ms 6428 KB Output is correct
69 Correct 480 ms 6356 KB Output is correct
70 Correct 453 ms 6416 KB Output is correct
71 Correct 476 ms 6416 KB Output is correct
72 Correct 454 ms 6416 KB Output is correct
73 Correct 460 ms 6692 KB Output is correct
74 Correct 489 ms 6724 KB Output is correct
75 Correct 530 ms 6684 KB Output is correct
76 Correct 501 ms 6684 KB Output is correct
77 Correct 495 ms 6684 KB Output is correct
78 Correct 496 ms 6664 KB Output is correct
79 Correct 462 ms 6648 KB Output is correct
80 Correct 469 ms 6764 KB Output is correct
81 Correct 483 ms 6732 KB Output is correct
82 Correct 474 ms 6736 KB Output is correct
83 Correct 518 ms 6612 KB Output is correct
84 Correct 495 ms 6736 KB Output is correct
85 Correct 534 ms 6612 KB Output is correct
86 Correct 515 ms 6732 KB Output is correct
87 Correct 500 ms 6612 KB Output is correct
88 Correct 515 ms 6552 KB Output is correct
89 Correct 509 ms 6552 KB Output is correct
90 Correct 517 ms 6552 KB Output is correct
91 Correct 512 ms 6560 KB Output is correct
92 Correct 534 ms 6604 KB Output is correct