답안 #629688

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
629688	2022-08-14T22:14:35 Z	54skyxenon	Mecho (IOI09_mecho)	C++17	100 / 100	254 ms	6552 KB

mecho

// From https://usaco.guide/problems/ioi-2009mecho/solution
 
#include <bits/stdc++.h>
using namespace std;

#define pii pair<int, int>
#define 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<pii> 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};

    vector<vector<bool>> bees_visited(n, vector<bool>(n));
	vector<vector<int>> bees_time(n, vector<int>(n));

    // move bees
    queue<pii> q;
	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;
			}
		}
	}
 
	// binary search on waiting time
	int l = 0;
	int r = n * n;
	while (l <= r) {
		vector<vector<bool>> mecho_visited(n, vector<bool>(n));
		vector<vector<int>> mecho_time(n, vector<int>(n));
		
		int eating_time = (l + r) / 2;
		
		// 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:80:23: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
   80 |   mecho_visited[mechox][mechoy] = true;
      |                       ^
mecho.cpp:111:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  111 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:111:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  111 |    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	212 KB	Output is correct
2	Correct	0 ms	212 KB	Output is correct
3	Correct	0 ms	212 KB	Output is correct
4	Correct	1 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	125 ms	6440 KB	Output is correct
8	Correct	0 ms	224 KB	Output is correct
9	Correct	0 ms	212 KB	Output is correct
10	Correct	0 ms	212 KB	Output is correct
11	Correct	0 ms	212 KB	Output is correct
12	Correct	1 ms	340 KB	Output is correct
13	Correct	1 ms	340 KB	Output is correct
14	Correct	1 ms	340 KB	Output is correct
15	Correct	0 ms	212 KB	Output is correct
16	Correct	1 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	212 KB	Output is correct
21	Correct	1 ms	340 KB	Output is correct
22	Correct	1 ms	348 KB	Output is correct
23	Correct	1 ms	340 KB	Output is correct
24	Correct	1 ms	340 KB	Output is correct
25	Correct	1 ms	340 KB	Output is correct
26	Correct	1 ms	340 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	1 ms	340 KB	Output is correct
31	Correct	1 ms	340 KB	Output is correct
32	Correct	1 ms	340 KB	Output is correct
33	Correct	10 ms	1536 KB	Output is correct
34	Correct	10 ms	1536 KB	Output is correct
35	Correct	31 ms	1544 KB	Output is correct
36	Correct	14 ms	1840 KB	Output is correct
37	Correct	16 ms	1868 KB	Output is correct
38	Correct	40 ms	1876 KB	Output is correct
39	Correct	17 ms	2252 KB	Output is correct
40	Correct	16 ms	2300 KB	Output is correct
41	Correct	53 ms	2296 KB	Output is correct
42	Correct	19 ms	2908 KB	Output is correct
43	Correct	24 ms	2904 KB	Output is correct
44	Correct	68 ms	2916 KB	Output is correct
45	Correct	23 ms	3420 KB	Output is correct
46	Correct	25 ms	3396 KB	Output is correct
47	Correct	82 ms	3380 KB	Output is correct
48	Correct	29 ms	3936 KB	Output is correct
49	Correct	28 ms	3908 KB	Output is correct
50	Correct	91 ms	4004 KB	Output is correct
51	Correct	30 ms	4532 KB	Output is correct
52	Correct	34 ms	4516 KB	Output is correct
53	Correct	132 ms	4664 KB	Output is correct
54	Correct	46 ms	5064 KB	Output is correct
55	Correct	49 ms	5052 KB	Output is correct
56	Correct	142 ms	5056 KB	Output is correct
57	Correct	41 ms	5744 KB	Output is correct
58	Correct	46 ms	5724 KB	Output is correct
59	Correct	173 ms	5820 KB	Output is correct
60	Correct	47 ms	6440 KB	Output is correct
61	Correct	51 ms	6428 KB	Output is correct
62	Correct	182 ms	6452 KB	Output is correct
63	Correct	161 ms	6416 KB	Output is correct
64	Correct	254 ms	6468 KB	Output is correct
65	Correct	189 ms	6444 KB	Output is correct
66	Correct	160 ms	6388 KB	Output is correct
67	Correct	170 ms	6412 KB	Output is correct
68	Correct	89 ms	6448 KB	Output is correct
69	Correct	75 ms	6432 KB	Output is correct
70	Correct	66 ms	6436 KB	Output is correct
71	Correct	69 ms	6428 KB	Output is correct
72	Correct	55 ms	6432 KB	Output is correct
73	Correct	63 ms	6476 KB	Output is correct
74	Correct	104 ms	6424 KB	Output is correct
75	Correct	137 ms	6528 KB	Output is correct
76	Correct	115 ms	6444 KB	Output is correct
77	Correct	96 ms	6468 KB	Output is correct
78	Correct	115 ms	6444 KB	Output is correct
79	Correct	84 ms	6456 KB	Output is correct
80	Correct	118 ms	6440 KB	Output is correct
81	Correct	113 ms	6440 KB	Output is correct
82	Correct	97 ms	6456 KB	Output is correct
83	Correct	125 ms	6436 KB	Output is correct
84	Correct	113 ms	6472 KB	Output is correct
85	Correct	125 ms	6444 KB	Output is correct
86	Correct	123 ms	6460 KB	Output is correct
87	Correct	122 ms	6444 KB	Output is correct
88	Correct	138 ms	6484 KB	Output is correct
89	Correct	132 ms	6456 KB	Output is correct
90	Correct	124 ms	6552 KB	Output is correct
91	Correct	123 ms	6488 KB	Output is correct
92	Correct	145 ms	6456 KB	Output is correct