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Submission #629684

# Submission time Handle Problem Language Result Execution time Memory
629684 2022-08-14T22:02:45 Z 54skyxenon Mecho (IOI09_mecho) C++17
89 / 100
 532 ms 11664 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, false));
vector<vector<int>> bees_time(MAX_N, vector<int>(MAX_N, 0));

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, false));
	vector<vector<int>> mecho_time(n, vector<int>(n, 0));
    
    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 2 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 3 ms 5460 KB Output is correct
5 Correct 3 ms 5460 KB Output is correct
6 Correct 3 ms 5460 KB Output is correct
7 Correct 167 ms 11472 KB Output is correct
8 Correct 3 ms 5460 KB Output is correct
9 Correct 3 ms 5460 KB Output is correct
10 Correct 3 ms 5460 KB Output is correct
11 Correct 3 ms 5460 KB Output is correct
12 Correct 3 ms 5484 KB Output is correct
13 Incorrect 3 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 5404 KB Output is correct
23 Correct 3 ms 5460 KB Output is correct
24 Correct 4 ms 5460 KB Output is correct
25 Correct 3 ms 5472 KB Output is correct
26 Correct 3 ms 5460 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 3 ms 5460 KB Output is correct
31 Correct 3 ms 5460 KB Output is correct
32 Correct 3 ms 5460 KB Output is correct
33 Correct 18 ms 6664 KB Output is correct
34 Correct 18 ms 6664 KB Output is correct
35 Correct 39 ms 6664 KB Output is correct
36 Correct 22 ms 7056 KB Output is correct
37 Correct 27 ms 7064 KB Output is correct
38 Correct 52 ms 6988 KB Output is correct
39 Correct 25 ms 7412 KB Output is correct
40 Correct 31 ms 7404 KB Output is correct
41 Correct 69 ms 7364 KB Output is correct
42 Correct 37 ms 8100 KB Output is correct
43 Correct 37 ms 8076 KB Output is correct
44 Correct 80 ms 8028 KB Output is correct
45 Correct 43 ms 8544 KB Output is correct
46 Correct 44 ms 8524 KB Output is correct
47 Correct 120 ms 8624 KB Output is correct
48 Correct 49 ms 9140 KB Output is correct
49 Correct 52 ms 9044 KB Output is correct
50 Correct 104 ms 8988 KB Output is correct
51 Correct 56 ms 9628 KB Output is correct
52 Correct 58 ms 9640 KB Output is correct
53 Correct 166 ms 9548 KB Output is correct
54 Correct 101 ms 10412 KB Output is correct
55 Correct 87 ms 10140 KB Output is correct
56 Correct 187 ms 10160 KB Output is correct
57 Correct 79 ms 10840 KB Output is correct
58 Correct 114 ms 10876 KB Output is correct
59 Correct 235 ms 10784 KB Output is correct
60 Correct 84 ms 11516 KB Output is correct
61 Correct 84 ms 11480 KB Output is correct
62 Correct 223 ms 11504 KB Output is correct
63 Correct 214 ms 11440 KB Output is correct
64 Correct 532 ms 11664 KB Output is correct
65 Correct 311 ms 11444 KB Output is correct
66 Correct 257 ms 11468 KB Output is correct
67 Correct 201 ms 11496 KB Output is correct
68 Correct 109 ms 11524 KB Output is correct
69 Correct 144 ms 11472 KB Output is correct
70 Correct 130 ms 11472 KB Output is correct
71 Correct 155 ms 11484 KB Output is correct
72 Incorrect 89 ms 11536 KB Output isn't correct
73 Incorrect 115 ms 11560 KB Output isn't correct
74 Correct 161 ms 11568 KB Output is correct
75 Correct 199 ms 11568 KB Output is correct
76 Correct 155 ms 11544 KB Output is correct
77 Correct 81 ms 11584 KB Output is correct
78 Correct 180 ms 11516 KB Output is correct
79 Correct 152 ms 11524 KB Output is correct
80 Correct 140 ms 11568 KB Output is correct
81 Correct 168 ms 11508 KB Output is correct
82 Correct 161 ms 11528 KB Output is correct
83 Correct 151 ms 11516 KB Output is correct
84 Correct 181 ms 11516 KB Output is correct
85 Correct 224 ms 11560 KB Output is correct
86 Correct 180 ms 11564 KB Output is correct
87 Correct 175 ms 11580 KB Output is correct
88 Correct 156 ms 11508 KB Output is correct
89 Correct 139 ms 11428 KB Output is correct
90 Correct 169 ms 11536 KB Output is correct
91 Correct 187 ms 11488 KB Output is correct
92 Correct 183 ms 11496 KB Output is correct