답안 #492249

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
492249	2021-12-06T08:01:15 Z	nehasane	Mecho (IOI09_mecho)	C++14	100 / 100	646 ms	6804 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	0 ms	204 KB	Output is correct
6	Correct	0 ms	204 KB	Output is correct
7	Correct	523 ms	6476 KB	Output is correct
8	Correct	1 ms	204 KB	Output is correct
9	Correct	0 ms	204 KB	Output is correct
10	Correct	0 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	3 ms	332 KB	Output is correct
15	Correct	0 ms	332 KB	Output is correct
16	Correct	0 ms	204 KB	Output is correct
17	Correct	0 ms	204 KB	Output is correct
18	Correct	0 ms	332 KB	Output is correct
19	Correct	1 ms	332 KB	Output is correct
20	Correct	0 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	1 ms	332 KB	Output is correct
27	Correct	1 ms	332 KB	Output is correct
28	Correct	1 ms	332 KB	Output is correct
29	Correct	1 ms	332 KB	Output is correct
30	Correct	1 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	41 ms	1540 KB	Output is correct
34	Correct	40 ms	1548 KB	Output is correct
35	Correct	74 ms	1524 KB	Output is correct
36	Correct	50 ms	1888 KB	Output is correct
37	Correct	53 ms	1864 KB	Output is correct
38	Correct	94 ms	1868 KB	Output is correct
39	Correct	74 ms	2268 KB	Output is correct
40	Correct	65 ms	2248 KB	Output is correct
41	Correct	127 ms	2124 KB	Output is correct
42	Correct	84 ms	2908 KB	Output is correct
43	Correct	84 ms	2900 KB	Output is correct
44	Correct	160 ms	2896 KB	Output is correct
45	Correct	106 ms	3376 KB	Output is correct
46	Correct	102 ms	3364 KB	Output is correct
47	Correct	189 ms	3364 KB	Output is correct
48	Correct	118 ms	3904 KB	Output is correct
49	Correct	129 ms	3916 KB	Output is correct
50	Correct	225 ms	3788 KB	Output is correct
51	Correct	146 ms	4460 KB	Output is correct
52	Correct	146 ms	4460 KB	Output is correct
53	Correct	282 ms	4440 KB	Output is correct
54	Correct	177 ms	5056 KB	Output is correct
55	Correct	169 ms	5060 KB	Output is correct
56	Correct	345 ms	5048 KB	Output is correct
57	Correct	195 ms	5704 KB	Output is correct
58	Correct	197 ms	5704 KB	Output is correct
59	Correct	407 ms	5780 KB	Output is correct
60	Correct	253 ms	6384 KB	Output is correct
61	Correct	235 ms	6580 KB	Output is correct
62	Correct	436 ms	6380 KB	Output is correct
63	Correct	509 ms	6376 KB	Output is correct
64	Correct	646 ms	6380 KB	Output is correct
65	Correct	574 ms	6384 KB	Output is correct
66	Correct	553 ms	6440 KB	Output is correct
67	Correct	525 ms	6508 KB	Output is correct
68	Correct	463 ms	6408 KB	Output is correct
69	Correct	496 ms	6536 KB	Output is correct
70	Correct	461 ms	6412 KB	Output is correct
71	Correct	486 ms	6468 KB	Output is correct
72	Correct	441 ms	6348 KB	Output is correct
73	Correct	464 ms	6700 KB	Output is correct
74	Correct	504 ms	6684 KB	Output is correct
75	Correct	540 ms	6704 KB	Output is correct
76	Correct	501 ms	6724 KB	Output is correct
77	Correct	508 ms	6804 KB	Output is correct
78	Correct	492 ms	6640 KB	Output is correct
79	Correct	490 ms	6676 KB	Output is correct
80	Correct	475 ms	6640 KB	Output is correct
81	Correct	497 ms	6648 KB	Output is correct
82	Correct	475 ms	6724 KB	Output is correct
83	Correct	521 ms	6600 KB	Output is correct
84	Correct	516 ms	6652 KB	Output is correct
85	Correct	534 ms	6604 KB	Output is correct
86	Correct	520 ms	6608 KB	Output is correct
87	Correct	528 ms	6736 KB	Output is correct
88	Correct	512 ms	6548 KB	Output is correct
89	Correct	511 ms	6596 KB	Output is correct
90	Correct	516 ms	6548 KB	Output is correct
91	Correct	533 ms	6548 KB	Output is correct
92	Correct	547 ms	6600 KB	Output is correct