Submission #697005

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
697005	2023-02-07T21:47:35 Z	MarwenElarbi	Mecho (IOI09_mecho)	C++14	100 / 100	642 ms	6872 KB

mecho

#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	1 ms	212 KB	Output is correct
2	Correct	1 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	1 ms	324 KB	Output is correct
6	Correct	1 ms	212 KB	Output is correct
7	Correct	532 ms	6628 KB	Output is correct
8	Correct	1 ms	212 KB	Output is correct
9	Correct	1 ms	212 KB	Output is correct
10	Correct	1 ms	320 KB	Output is correct
11	Correct	1 ms	212 KB	Output is correct
12	Correct	2 ms	324 KB	Output is correct
13	Correct	2 ms	340 KB	Output is correct
14	Correct	3 ms	340 KB	Output is correct
15	Correct	1 ms	320 KB	Output is correct
16	Correct	1 ms	212 KB	Output is correct
17	Correct	1 ms	340 KB	Output is correct
18	Correct	1 ms	324 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	2 ms	320 KB	Output is correct
26	Correct	2 ms	320 KB	Output is correct
27	Correct	1 ms	340 KB	Output is correct
28	Correct	1 ms	340 KB	Output is correct
29	Correct	1 ms	340 KB	Output is correct
30	Correct	2 ms	336 KB	Output is correct
31	Correct	2 ms	340 KB	Output is correct
32	Correct	2 ms	340 KB	Output is correct
33	Correct	40 ms	1680 KB	Output is correct
34	Correct	41 ms	1624 KB	Output is correct
35	Correct	75 ms	1524 KB	Output is correct
36	Correct	51 ms	2024 KB	Output is correct
37	Correct	56 ms	2012 KB	Output is correct
38	Correct	96 ms	2004 KB	Output is correct
39	Correct	64 ms	2368 KB	Output is correct
40	Correct	67 ms	2272 KB	Output is correct
41	Correct	130 ms	2264 KB	Output is correct
42	Correct	86 ms	2976 KB	Output is correct
43	Correct	83 ms	2916 KB	Output is correct
44	Correct	159 ms	3032 KB	Output is correct
45	Correct	106 ms	3524 KB	Output is correct
46	Correct	100 ms	3540 KB	Output is correct
47	Correct	195 ms	3492 KB	Output is correct
48	Correct	135 ms	3932 KB	Output is correct
49	Correct	128 ms	3920 KB	Output is correct
50	Correct	224 ms	4044 KB	Output is correct
51	Correct	152 ms	4604 KB	Output is correct
52	Correct	145 ms	4588 KB	Output is correct
53	Correct	284 ms	4476 KB	Output is correct
54	Correct	179 ms	5208 KB	Output is correct
55	Correct	170 ms	5192 KB	Output is correct
56	Correct	339 ms	5184 KB	Output is correct
57	Correct	214 ms	5712 KB	Output is correct
58	Correct	224 ms	5964 KB	Output is correct
59	Correct	390 ms	5828 KB	Output is correct
60	Correct	237 ms	6400 KB	Output is correct
61	Correct	223 ms	6664 KB	Output is correct
62	Correct	473 ms	6632 KB	Output is correct
63	Correct	500 ms	6568 KB	Output is correct
64	Correct	642 ms	6524 KB	Output is correct
65	Correct	573 ms	6608 KB	Output is correct
66	Correct	545 ms	6648 KB	Output is correct
67	Correct	587 ms	6516 KB	Output is correct
68	Correct	474 ms	6604 KB	Output is correct
69	Correct	513 ms	6544 KB	Output is correct
70	Correct	459 ms	6548 KB	Output is correct
71	Correct	486 ms	6672 KB	Output is correct
72	Correct	458 ms	6540 KB	Output is correct
73	Correct	534 ms	6816 KB	Output is correct
74	Correct	516 ms	6824 KB	Output is correct
75	Correct	563 ms	6872 KB	Output is correct
76	Correct	513 ms	6820 KB	Output is correct
77	Correct	518 ms	6752 KB	Output is correct
78	Correct	495 ms	6740 KB	Output is correct
79	Correct	466 ms	6784 KB	Output is correct
80	Correct	494 ms	6716 KB	Output is correct
81	Correct	494 ms	6860 KB	Output is correct
82	Correct	493 ms	6852 KB	Output is correct
83	Correct	514 ms	6612 KB	Output is correct
84	Correct	512 ms	6860 KB	Output is correct
85	Correct	547 ms	6744 KB	Output is correct
86	Correct	533 ms	6736 KB	Output is correct
87	Correct	519 ms	6860 KB	Output is correct
88	Correct	536 ms	6684 KB	Output is correct
89	Correct	507 ms	6676 KB	Output is correct
90	Correct	521 ms	6748 KB	Output is correct
91	Correct	526 ms	6732 KB	Output is correct
92	Correct	535 ms	6680 KB	Output is correct