답안 #492247

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
492247	2021-12-06T07:54:34 Z	nehasane	Mecho (IOI09_mecho)	C++14	100 / 100	627 ms	7396 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

#	결과	실행 시간	메모리	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