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Submission #629683

# Submission time Handle Problem Language Result Execution time Memory
629683 2022-08-14T22:01:50 Z 54skyxenon Mecho (IOI09_mecho) C++17
89 / 100
 454 ms 11668 KB 
// https://oj.uz/problem/view/IOI09_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
#define int long long

vector<string> field(MAX_N);
int n, s;
int mechox, mechoy, home_x, home_y;

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

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};

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;
}

bool ok(int eating_time) {
    vector<vector<bool>> mecho_visited(n, vector<bool>(n));
	vector<vector<int>> mecho_time(n, vector<int>(n));
    
    queue<pii> q({{mechox, mechoy}});

	// 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
	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]) {
			return true;
		}
	}

    return false;
}

int bs(int lo, int hi) {
    if (lo > hi) {
        return -1;
    }

    int mid = (lo + hi) / 2;

    if (!ok(mid)) {
        return bs(lo, mid - 1);
    }
    else if (mid < hi && ok(mid + 1)) {
        return bs(mid + 1, hi);
    }
    else {
        return mid;
    }
}

int32_t main() {
	cin >> n >> s;
	for (int i = 0; i < n; i++) {
		cin >> field[i];
	}
	
	vector<pii> hives;
	// 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;
			}
		}
	}

    // move bees
    queue<pii> q;
	for (auto& [x, y] : hives) {
		q.push({x, y});
		bees_visited[x][y] = 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;
			}
		}
	}

	cout << bs(0, n * n) << '\n';
}

Subtask #1
89.0 / 100.0

# Verdict Execution time Memory Grader output
1 Correct 3 ms 5460 KB Output is correct
2 Correct 3 ms 5460 KB Output is correct
3 Correct 3 ms 5460 KB Output is correct
4 Correct 2 ms 5460 KB Output is correct
5 Correct 3 ms 5388 KB Output is correct
6 Correct 3 ms 5460 KB Output is correct
7 Correct 176 ms 11468 KB Output is correct
8 Correct 3 ms 5460 KB Output is correct
9 Correct 3 ms 5460 KB Output is correct
10 Correct 4 ms 5460 KB Output is correct
11 Correct 3 ms 5396 KB Output is correct
12 Correct 3 ms 5460 KB Output is correct
13 Incorrect 5 ms 5460 KB Output isn't correct
14 Correct 3 ms 5460 KB Output is correct
15 Correct 3 ms 5460 KB Output is correct
16 Correct 3 ms 5460 KB Output is correct
17 Correct 3 ms 5460 KB Output is correct
18 Correct 3 ms 5460 KB Output is correct
19 Correct 3 ms 5460 KB Output is correct
20 Correct 3 ms 5460 KB Output is correct
21 Correct 3 ms 5460 KB Output is correct
22 Correct 3 ms 5460 KB Output is correct
23 Correct 3 ms 5460 KB Output is correct
24 Correct 3 ms 5456 KB Output is correct
25 Correct 4 ms 5436 KB Output is correct
26 Correct 3 ms 5412 KB Output is correct
27 Correct 3 ms 5460 KB Output is correct
28 Correct 3 ms 5460 KB Output is correct
29 Correct 3 ms 5460 KB Output is correct
30 Correct 4 ms 5460 KB Output is correct
31 Correct 4 ms 5460 KB Output is correct
32 Correct 4 ms 5460 KB Output is correct
33 Correct 19 ms 6672 KB Output is correct
34 Correct 18 ms 6760 KB Output is correct
35 Correct 40 ms 6692 KB Output is correct
36 Correct 21 ms 6992 KB Output is correct
37 Correct 24 ms 6988 KB Output is correct
38 Correct 48 ms 7012 KB Output is correct
39 Correct 25 ms 7436 KB Output is correct
40 Correct 29 ms 7420 KB Output is correct
41 Correct 69 ms 7360 KB Output is correct
42 Correct 38 ms 8080 KB Output is correct
43 Correct 38 ms 8084 KB Output is correct
44 Correct 80 ms 8004 KB Output is correct
45 Correct 45 ms 8632 KB Output is correct
46 Correct 41 ms 8504 KB Output is correct
47 Correct 93 ms 8480 KB Output is correct
48 Correct 51 ms 9024 KB Output is correct
49 Correct 59 ms 9028 KB Output is correct
50 Correct 94 ms 8980 KB Output is correct
51 Correct 59 ms 9700 KB Output is correct
52 Correct 62 ms 9560 KB Output is correct
53 Correct 152 ms 9644 KB Output is correct
54 Correct 81 ms 10260 KB Output is correct
55 Correct 76 ms 10208 KB Output is correct
56 Correct 169 ms 10224 KB Output is correct
57 Correct 78 ms 10832 KB Output is correct
58 Correct 89 ms 10820 KB Output is correct
59 Correct 200 ms 10784 KB Output is correct
60 Correct 93 ms 11496 KB Output is correct
61 Correct 86 ms 11548 KB Output is correct
62 Correct 250 ms 11484 KB Output is correct
63 Correct 166 ms 11460 KB Output is correct
64 Correct 454 ms 11472 KB Output is correct
65 Correct 279 ms 11628 KB Output is correct
66 Correct 267 ms 11456 KB Output is correct
67 Correct 189 ms 11496 KB Output is correct
68 Correct 94 ms 11480 KB Output is correct
69 Correct 125 ms 11668 KB Output is correct
70 Correct 85 ms 11496 KB Output is correct
71 Correct 111 ms 11492 KB Output is correct
72 Incorrect 91 ms 11508 KB Output isn't correct
73 Incorrect 101 ms 11564 KB Output isn't correct
74 Correct 133 ms 11588 KB Output is correct
75 Correct 182 ms 11536 KB Output is correct
76 Correct 137 ms 11528 KB Output is correct
77 Correct 79 ms 11560 KB Output is correct
78 Correct 137 ms 11544 KB Output is correct
79 Correct 138 ms 11516 KB Output is correct
80 Correct 132 ms 11512 KB Output is correct
81 Correct 143 ms 11556 KB Output is correct
82 Correct 146 ms 11508 KB Output is correct
83 Correct 136 ms 11596 KB Output is correct
84 Correct 144 ms 11560 KB Output is correct
85 Correct 187 ms 11512 KB Output is correct
86 Correct 140 ms 11588 KB Output is correct
87 Correct 158 ms 11500 KB Output is correct
88 Correct 139 ms 11508 KB Output is correct
89 Correct 139 ms 11504 KB Output is correct
90 Correct 153 ms 11472 KB Output is correct
91 Correct 181 ms 11500 KB Output is correct
92 Correct 199 ms 11476 KB Output is correct