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Submission #492248

# Submission time Handle Problem Language Result Execution time Memory
492248 2021-12-06T07:58:16 Z nehasane Mecho (IOI09_mecho) C++14
100 / 100
 635 ms 6768 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 0 ms 204 KB Output is correct
6 Correct 0 ms 204 KB Output is correct
7 Correct 529 ms 6500 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 1 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 3 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 204 KB Output is correct
18 Correct 0 ms 332 KB Output is correct
19 Correct 1 ms 204 KB Output is correct
20 Correct 1 ms 332 KB Output is correct
21 Correct 2 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 2 ms 332 KB Output is correct
26 Correct 2 ms 332 KB Output is correct
27 Correct 2 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 42 ms 1556 KB Output is correct
34 Correct 39 ms 1528 KB Output is correct
35 Correct 73 ms 1520 KB Output is correct
36 Correct 52 ms 1916 KB Output is correct
37 Correct 55 ms 1872 KB Output is correct
38 Correct 94 ms 1792 KB Output is correct
39 Correct 67 ms 2252 KB Output is correct
40 Correct 69 ms 2256 KB Output is correct
41 Correct 131 ms 2236 KB Output is correct
42 Correct 85 ms 2904 KB Output is correct
43 Correct 87 ms 2892 KB Output is correct
44 Correct 165 ms 2892 KB Output is correct
45 Correct 107 ms 3368 KB Output is correct
46 Correct 110 ms 3368 KB Output is correct
47 Correct 191 ms 3276 KB Output is correct
48 Correct 142 ms 3896 KB Output is correct
49 Correct 125 ms 3912 KB Output is correct
50 Correct 224 ms 3796 KB Output is correct
51 Correct 150 ms 4468 KB Output is correct
52 Correct 144 ms 4448 KB Output is correct
53 Correct 281 ms 4436 KB Output is correct
54 Correct 175 ms 5072 KB Output is correct
55 Correct 171 ms 5084 KB Output is correct
56 Correct 351 ms 5068 KB Output is correct
57 Correct 194 ms 5700 KB Output is correct
58 Correct 197 ms 5716 KB Output is correct
59 Correct 378 ms 5708 KB Output is correct
60 Correct 257 ms 6628 KB Output is correct
61 Correct 237 ms 6392 KB Output is correct
62 Correct 440 ms 6380 KB Output is correct
63 Correct 512 ms 6376 KB Output is correct
64 Correct 635 ms 6504 KB Output is correct
65 Correct 575 ms 6432 KB Output is correct
66 Correct 537 ms 6380 KB Output is correct
67 Correct 515 ms 6392 KB Output is correct
68 Correct 478 ms 6412 KB Output is correct
69 Correct 497 ms 6404 KB Output is correct
70 Correct 466 ms 6492 KB Output is correct
71 Correct 470 ms 6348 KB Output is correct
72 Correct 445 ms 6468 KB Output is correct
73 Correct 489 ms 6676 KB Output is correct
74 Correct 495 ms 6728 KB Output is correct
75 Correct 541 ms 6680 KB Output is correct
76 Correct 494 ms 6676 KB Output is correct
77 Correct 508 ms 6684 KB Output is correct
78 Correct 486 ms 6604 KB Output is correct
79 Correct 477 ms 6640 KB Output is correct
80 Correct 466 ms 6640 KB Output is correct
81 Correct 488 ms 6644 KB Output is correct
82 Correct 477 ms 6768 KB Output is correct
83 Correct 501 ms 6600 KB Output is correct
84 Correct 516 ms 6608 KB Output is correct
85 Correct 523 ms 6608 KB Output is correct
86 Correct 509 ms 6604 KB Output is correct
87 Correct 533 ms 6600 KB Output is correct
88 Correct 498 ms 6452 KB Output is correct
89 Correct 517 ms 6540 KB Output is correct
90 Correct 499 ms 6476 KB Output is correct
91 Correct 510 ms 6544 KB Output is correct
92 Correct 553 ms 6552 KB Output is correct