답안 #629689

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
629689	2022-08-14T22:16:17 Z	54skyxenon	Mecho (IOI09_mecho)	C++17	100 / 100	245 ms	6580 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;

vector<vector<bool>> bees_visited(MAX_N, vector<bool>(MAX_N));
vector<vector<int>> bees_time(MAX_N, vector<int>(MAX_N));
 
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};

    // 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	2 ms	2900 KB	Output is correct
2	Correct	2 ms	2900 KB	Output is correct
3	Correct	2 ms	2900 KB	Output is correct
4	Correct	2 ms	2900 KB	Output is correct
5	Correct	2 ms	2900 KB	Output is correct
6	Correct	2 ms	2900 KB	Output is correct
7	Correct	125 ms	6448 KB	Output is correct
8	Correct	2 ms	2900 KB	Output is correct
9	Correct	2 ms	2900 KB	Output is correct
10	Correct	2 ms	2900 KB	Output is correct
11	Correct	2 ms	2900 KB	Output is correct
12	Correct	2 ms	2900 KB	Output is correct
13	Correct	2 ms	2900 KB	Output is correct
14	Correct	2 ms	2900 KB	Output is correct
15	Correct	2 ms	2900 KB	Output is correct
16	Correct	2 ms	2900 KB	Output is correct
17	Correct	2 ms	2900 KB	Output is correct
18	Correct	2 ms	2900 KB	Output is correct
19	Correct	2 ms	2900 KB	Output is correct
20	Correct	2 ms	2900 KB	Output is correct
21	Correct	2 ms	2900 KB	Output is correct
22	Correct	2 ms	2996 KB	Output is correct
23	Correct	3 ms	2900 KB	Output is correct
24	Correct	2 ms	2900 KB	Output is correct
25	Correct	2 ms	2900 KB	Output is correct
26	Correct	2 ms	2900 KB	Output is correct
27	Correct	2 ms	2900 KB	Output is correct
28	Correct	2 ms	2900 KB	Output is correct
29	Correct	2 ms	2900 KB	Output is correct
30	Correct	3 ms	2900 KB	Output is correct
31	Correct	2 ms	2900 KB	Output is correct
32	Correct	2 ms	2900 KB	Output is correct
33	Correct	10 ms	3732 KB	Output is correct
34	Correct	12 ms	3664 KB	Output is correct
35	Correct	31 ms	3728 KB	Output is correct
36	Correct	13 ms	3796 KB	Output is correct
37	Correct	14 ms	3832 KB	Output is correct
38	Correct	42 ms	3848 KB	Output is correct
39	Correct	15 ms	4052 KB	Output is correct
40	Correct	16 ms	4052 KB	Output is correct
41	Correct	58 ms	4088 KB	Output is correct
42	Correct	22 ms	4544 KB	Output is correct
43	Correct	21 ms	4504 KB	Output is correct
44	Correct	68 ms	4500 KB	Output is correct
45	Correct	23 ms	4756 KB	Output is correct
46	Correct	24 ms	4796 KB	Output is correct
47	Correct	78 ms	4812 KB	Output is correct
48	Correct	27 ms	5092 KB	Output is correct
49	Correct	28 ms	5104 KB	Output is correct
50	Correct	94 ms	5060 KB	Output is correct
51	Correct	31 ms	5388 KB	Output is correct
52	Correct	33 ms	5388 KB	Output is correct
53	Correct	118 ms	5396 KB	Output is correct
54	Correct	37 ms	5716 KB	Output is correct
55	Correct	39 ms	5708 KB	Output is correct
56	Correct	134 ms	5672 KB	Output is correct
57	Correct	44 ms	6068 KB	Output is correct
58	Correct	45 ms	6064 KB	Output is correct
59	Correct	152 ms	6040 KB	Output is correct
60	Correct	47 ms	6428 KB	Output is correct
61	Correct	50 ms	6448 KB	Output is correct
62	Correct	174 ms	6392 KB	Output is correct
63	Correct	140 ms	6408 KB	Output is correct
64	Correct	245 ms	6428 KB	Output is correct
65	Correct	193 ms	6404 KB	Output is correct
66	Correct	172 ms	6436 KB	Output is correct
67	Correct	154 ms	6400 KB	Output is correct
68	Correct	78 ms	6448 KB	Output is correct
69	Correct	87 ms	6432 KB	Output is correct
70	Correct	62 ms	6436 KB	Output is correct
71	Correct	69 ms	6516 KB	Output is correct
72	Correct	56 ms	6496 KB	Output is correct
73	Correct	64 ms	6460 KB	Output is correct
74	Correct	106 ms	6516 KB	Output is correct
75	Correct	113 ms	6508 KB	Output is correct
76	Correct	103 ms	6552 KB	Output is correct
77	Correct	101 ms	6484 KB	Output is correct
78	Correct	112 ms	6428 KB	Output is correct
79	Correct	82 ms	6376 KB	Output is correct
80	Correct	96 ms	6432 KB	Output is correct
81	Correct	105 ms	6432 KB	Output is correct
82	Correct	98 ms	6460 KB	Output is correct
83	Correct	116 ms	6484 KB	Output is correct
84	Correct	109 ms	6420 KB	Output is correct
85	Correct	118 ms	6452 KB	Output is correct
86	Correct	119 ms	6580 KB	Output is correct
87	Correct	114 ms	6428 KB	Output is correct
88	Correct	121 ms	6452 KB	Output is correct
89	Correct	120 ms	6444 KB	Output is correct
90	Correct	129 ms	6420 KB	Output is correct
91	Correct	121 ms	6452 KB	Output is correct
92	Correct	132 ms	6448 KB	Output is correct