oj.uz

Submission #492247

# Submission time Handle Problem Language Result Execution time Memory
492247 2021-12-06T07:54:34 Z nehasane Mecho (IOI09_mecho) C++14
100 / 100
 627 ms 7396 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:77:31: warning: 'mechoy' may be used uninitialized in this function [-Wmaybe-uninitialized]
   77 |   mecho_visited[mechox][mechoy] = true;
      |                               ^
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 204 KB Output is correct
2 Correct 0 ms 204 KB Output is correct
3 Correct 0 ms 204 KB Output is correct
4 Correct 0 ms 204 KB Output is correct
5 Correct 1 ms 204 KB Output is correct
6 Correct 0 ms 204 KB Output is correct
7 Correct 509 ms 7120 KB Output is correct
8 Correct 1 ms 204 KB Output is correct
9 Correct 0 ms 204 KB Output is correct
10 Correct 1 ms 332 KB Output is correct
11 Correct 0 ms 332 KB Output is correct
12 Correct 1 ms 332 KB Output is correct
13 Correct 2 ms 332 KB Output is correct
14 Correct 2 ms 332 KB Output is correct
15 Correct 1 ms 332 KB Output is correct
16 Correct 1 ms 204 KB Output is correct
17 Correct 1 ms 332 KB Output is correct
18 Correct 1 ms 204 KB Output is correct
19 Correct 1 ms 332 KB Output is correct
20 Correct 1 ms 332 KB Output is correct
21 Correct 1 ms 332 KB Output is correct
22 Correct 1 ms 332 KB Output is correct
23 Correct 1 ms 332 KB Output is correct
24 Correct 1 ms 332 KB Output is correct
25 Correct 1 ms 332 KB Output is correct
26 Correct 2 ms 332 KB Output is correct
27 Correct 1 ms 316 KB Output is correct
28 Correct 1 ms 332 KB Output is correct
29 Correct 1 ms 332 KB Output is correct
30 Correct 2 ms 316 KB Output is correct
31 Correct 2 ms 332 KB Output is correct
32 Correct 3 ms 320 KB Output is correct
33 Correct 41 ms 1620 KB Output is correct
34 Correct 40 ms 1624 KB Output is correct
35 Correct 79 ms 1740 KB Output is correct
36 Correct 52 ms 2032 KB Output is correct
37 Correct 55 ms 2044 KB Output is correct
38 Correct 95 ms 2020 KB Output is correct
39 Correct 65 ms 2460 KB Output is correct
40 Correct 67 ms 2436 KB Output is correct
41 Correct 136 ms 2440 KB Output is correct
42 Correct 87 ms 3160 KB Output is correct
43 Correct 85 ms 3156 KB Output is correct
44 Correct 163 ms 3148 KB Output is correct
45 Correct 107 ms 3672 KB Output is correct
46 Correct 107 ms 3744 KB Output is correct
47 Correct 191 ms 3660 KB Output is correct
48 Correct 120 ms 4276 KB Output is correct
49 Correct 130 ms 4260 KB Output is correct
50 Correct 236 ms 4252 KB Output is correct
51 Correct 154 ms 4864 KB Output is correct
52 Correct 149 ms 4876 KB Output is correct
53 Correct 284 ms 4856 KB Output is correct
54 Correct 173 ms 5552 KB Output is correct
55 Correct 169 ms 5536 KB Output is correct
56 Correct 342 ms 5532 KB Output is correct
57 Correct 199 ms 6248 KB Output is correct
58 Correct 201 ms 6256 KB Output is correct
59 Correct 385 ms 6260 KB Output is correct
60 Correct 235 ms 7040 KB Output is correct
61 Correct 221 ms 7012 KB Output is correct
62 Correct 441 ms 7008 KB Output is correct
63 Correct 504 ms 7008 KB Output is correct
64 Correct 627 ms 7020 KB Output is correct
65 Correct 577 ms 7112 KB Output is correct
66 Correct 540 ms 7012 KB Output is correct
67 Correct 507 ms 6988 KB Output is correct
68 Correct 480 ms 7040 KB Output is correct
69 Correct 491 ms 7040 KB Output is correct
70 Correct 455 ms 7112 KB Output is correct
71 Correct 473 ms 6988 KB Output is correct
72 Correct 434 ms 7040 KB Output is correct
73 Correct 464 ms 7364 KB Output is correct
74 Correct 488 ms 7240 KB Output is correct
75 Correct 583 ms 7312 KB Output is correct
76 Correct 489 ms 7308 KB Output is correct
77 Correct 526 ms 7316 KB Output is correct
78 Correct 507 ms 7396 KB Output is correct
79 Correct 465 ms 7276 KB Output is correct
80 Correct 482 ms 7348 KB Output is correct
81 Correct 490 ms 7276 KB Output is correct
82 Correct 497 ms 7244 KB Output is correct
83 Correct 527 ms 7244 KB Output is correct
84 Correct 496 ms 7232 KB Output is correct
85 Correct 563 ms 7244 KB Output is correct
86 Correct 516 ms 7240 KB Output is correct
87 Correct 529 ms 7228 KB Output is correct
88 Correct 538 ms 7172 KB Output is correct
89 Correct 532 ms 7172 KB Output is correct
90 Correct 526 ms 7308 KB Output is correct
91 Correct 507 ms 7180 KB Output is correct
92 Correct 561 ms 7176 KB Output is correct