oj.uz

Submission #529633

# Submission time Handle Problem Language Result Execution time Memory
529633 2022-02-23T09:34:08 Z thezomb1e Mecho (IOI09_mecho) C++17
100 / 100
 635 ms 6852 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 1 ms 204 KB Output is correct
2 Correct 1 ms 204 KB Output is correct
3 Correct 1 ms 204 KB Output is correct
4 Correct 1 ms 204 KB Output is correct
5 Correct 0 ms 204 KB Output is correct
6 Correct 0 ms 204 KB Output is correct
7 Correct 531 ms 6488 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 204 KB Output is correct
11 Correct 0 ms 204 KB Output is correct
12 Correct 2 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 204 KB Output is correct
16 Correct 1 ms 332 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 332 KB Output is correct
28 Correct 2 ms 332 KB Output is correct
29 Correct 2 ms 332 KB Output is correct
30 Correct 2 ms 332 KB Output is correct
31 Correct 2 ms 332 KB Output is correct
32 Correct 2 ms 332 KB Output is correct
33 Correct 40 ms 1516 KB Output is correct
34 Correct 40 ms 1532 KB Output is correct
35 Correct 77 ms 1612 KB Output is correct
36 Correct 53 ms 1996 KB Output is correct
37 Correct 52 ms 1872 KB Output is correct
38 Correct 95 ms 1868 KB Output is correct
39 Correct 64 ms 2252 KB Output is correct
40 Correct 67 ms 2232 KB Output is correct
41 Correct 127 ms 2144 KB Output is correct
42 Correct 93 ms 3052 KB Output is correct
43 Correct 122 ms 2912 KB Output is correct
44 Correct 162 ms 2896 KB Output is correct
45 Correct 106 ms 3404 KB Output is correct
46 Correct 102 ms 3420 KB Output is correct
47 Correct 208 ms 3356 KB Output is correct
48 Correct 118 ms 3932 KB Output is correct
49 Correct 125 ms 3920 KB Output is correct
50 Correct 281 ms 3996 KB Output is correct
51 Correct 145 ms 4444 KB Output is correct
52 Correct 144 ms 4476 KB Output is correct
53 Correct 291 ms 4428 KB Output is correct
54 Correct 215 ms 5060 KB Output is correct
55 Correct 170 ms 5064 KB Output is correct
56 Correct 395 ms 5048 KB Output is correct
57 Correct 202 ms 5716 KB Output is correct
58 Correct 209 ms 5692 KB Output is correct
59 Correct 421 ms 5764 KB Output is correct
60 Correct 243 ms 6388 KB Output is correct
61 Correct 227 ms 6484 KB Output is correct
62 Correct 430 ms 6380 KB Output is correct
63 Correct 514 ms 6380 KB Output is correct
64 Correct 635 ms 6384 KB Output is correct
65 Correct 566 ms 6380 KB Output is correct
66 Correct 562 ms 6436 KB Output is correct
67 Correct 509 ms 6384 KB Output is correct
68 Correct 511 ms 6408 KB Output is correct
69 Correct 495 ms 6600 KB Output is correct
70 Correct 498 ms 6416 KB Output is correct
71 Correct 479 ms 6424 KB Output is correct
72 Correct 446 ms 6468 KB Output is correct
73 Correct 466 ms 6680 KB Output is correct
74 Correct 509 ms 6688 KB Output is correct
75 Correct 545 ms 6792 KB Output is correct
76 Correct 531 ms 6852 KB Output is correct
77 Correct 569 ms 6808 KB Output is correct
78 Correct 490 ms 6604 KB Output is correct
79 Correct 457 ms 6732 KB Output is correct
80 Correct 467 ms 6640 KB Output is correct
81 Correct 472 ms 6640 KB Output is correct
82 Correct 505 ms 6644 KB Output is correct
83 Correct 523 ms 6604 KB Output is correct
84 Correct 502 ms 6676 KB Output is correct
85 Correct 532 ms 6724 KB Output is correct
86 Correct 499 ms 6604 KB Output is correct
87 Correct 517 ms 6604 KB Output is correct
88 Correct 562 ms 6548 KB Output is correct
89 Correct 509 ms 6484 KB Output is correct
90 Correct 520 ms 6544 KB Output is correct
91 Correct 510 ms 6552 KB Output is correct
92 Correct 545 ms 6596 KB Output is correct