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Submission #629688

# Submission time Handle Problem Language Result Execution time Memory
629688 2022-08-14T22:14:35 Z 54skyxenon Mecho (IOI09_mecho) C++17
100 / 100
 254 ms 6552 KB 
// 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

# Verdict Execution time Memory 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