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Submission #599849

# Submission time Handle Problem Language Result Execution time Memory
599849 2022-07-20T02:13:27 Z alexz1205 Mecho (IOI09_mecho) C++14
100 / 100
 637 ms 6748 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 212 KB Output is correct
2 Correct 0 ms 212 KB Output is correct
3 Correct 1 ms 212 KB Output is correct
4 Correct 0 ms 212 KB Output is correct
5 Correct 0 ms 212 KB Output is correct
6 Correct 0 ms 212 KB Output is correct
7 Correct 570 ms 6500 KB Output is correct
8 Correct 1 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 340 KB Output is correct
15 Correct 1 ms 340 KB Output is correct
16 Correct 0 ms 212 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 2 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 2 ms 340 KB Output is correct
26 Correct 1 ms 364 KB Output is correct
27 Correct 1 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 43 ms 1588 KB Output is correct
34 Correct 43 ms 1536 KB Output is correct
35 Correct 76 ms 1532 KB Output is correct
36 Correct 54 ms 1988 KB Output is correct
37 Correct 53 ms 1888 KB Output is correct
38 Correct 100 ms 1876 KB Output is correct
39 Correct 62 ms 2268 KB Output is correct
40 Correct 72 ms 2400 KB Output is correct
41 Correct 134 ms 2248 KB Output is correct
42 Correct 90 ms 3156 KB Output is correct
43 Correct 89 ms 3012 KB Output is correct
44 Correct 205 ms 2900 KB Output is correct
45 Correct 111 ms 3380 KB Output is correct
46 Correct 100 ms 3380 KB Output is correct
47 Correct 186 ms 3372 KB Output is correct
48 Correct 128 ms 3908 KB Output is correct
49 Correct 128 ms 3916 KB Output is correct
50 Correct 241 ms 3916 KB Output is correct
51 Correct 176 ms 4468 KB Output is correct
52 Correct 157 ms 4516 KB Output is correct
53 Correct 282 ms 4456 KB Output is correct
54 Correct 192 ms 5072 KB Output is correct
55 Correct 185 ms 5068 KB Output is correct
56 Correct 343 ms 5076 KB Output is correct
57 Correct 209 ms 5696 KB Output is correct
58 Correct 189 ms 5716 KB Output is correct
59 Correct 430 ms 5616 KB Output is correct
60 Correct 233 ms 6404 KB Output is correct
61 Correct 222 ms 6384 KB Output is correct
62 Correct 495 ms 6348 KB Output is correct
63 Correct 502 ms 6392 KB Output is correct
64 Correct 637 ms 6392 KB Output is correct
65 Correct 568 ms 6412 KB Output is correct
66 Correct 580 ms 6428 KB Output is correct
67 Correct 504 ms 6392 KB Output is correct
68 Correct 485 ms 6416 KB Output is correct
69 Correct 499 ms 6416 KB Output is correct
70 Correct 454 ms 6476 KB Output is correct
71 Correct 477 ms 6548 KB Output is correct
72 Correct 449 ms 6416 KB Output is correct
73 Correct 507 ms 6732 KB Output is correct
74 Correct 508 ms 6688 KB Output is correct
75 Correct 580 ms 6748 KB Output is correct
76 Correct 564 ms 6688 KB Output is correct
77 Correct 512 ms 6688 KB Output is correct
78 Correct 502 ms 6656 KB Output is correct
79 Correct 477 ms 6696 KB Output is correct
80 Correct 482 ms 6652 KB Output is correct
81 Correct 494 ms 6648 KB Output is correct
82 Correct 494 ms 6704 KB Output is correct
83 Correct 538 ms 6500 KB Output is correct
84 Correct 518 ms 6612 KB Output is correct
85 Correct 525 ms 6612 KB Output is correct
86 Correct 556 ms 6736 KB Output is correct
87 Correct 512 ms 6616 KB Output is correct
88 Correct 515 ms 6576 KB Output is correct
89 Correct 533 ms 6548 KB Output is correct
90 Correct 524 ms 6560 KB Output is correct
91 Correct 545 ms 6604 KB Output is correct
92 Correct 594 ms 6680 KB Output is correct