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Submission #629682

# Submission time Handle Problem Language Result Execution time Memory
629682 2022-08-14T22:00:59 Z 54skyxenon Mecho (IOI09_mecho) C++17
89 / 100
 411 ms 6692 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

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;
    }
}

int 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 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 1 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 143 ms 6484 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 3 ms 2900 KB Output is correct
12 Correct 2 ms 2900 KB Output is correct
13 Incorrect 2 ms 2900 KB Output isn't 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 2900 KB Output is correct
23 Correct 2 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 2948 KB Output is correct
30 Correct 2 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 13 ms 3668 KB Output is correct
34 Correct 14 ms 3668 KB Output is correct
35 Correct 34 ms 3676 KB Output is correct
36 Correct 15 ms 3860 KB Output is correct
37 Correct 17 ms 3828 KB Output is correct
38 Correct 43 ms 3808 KB Output is correct
39 Correct 19 ms 4128 KB Output is correct
40 Correct 21 ms 4052 KB Output is correct
41 Correct 69 ms 4236 KB Output is correct
42 Correct 30 ms 4508 KB Output is correct
43 Correct 29 ms 4512 KB Output is correct
44 Correct 74 ms 4548 KB Output is correct
45 Correct 31 ms 4756 KB Output is correct
46 Correct 31 ms 4744 KB Output is correct
47 Correct 83 ms 4780 KB Output is correct
48 Correct 33 ms 5052 KB Output is correct
49 Correct 39 ms 5112 KB Output is correct
50 Correct 84 ms 5060 KB Output is correct
51 Correct 38 ms 5436 KB Output is correct
52 Correct 48 ms 5340 KB Output is correct
53 Correct 133 ms 5428 KB Output is correct
54 Correct 52 ms 5676 KB Output is correct
55 Correct 53 ms 5672 KB Output is correct
56 Correct 142 ms 5716 KB Output is correct
57 Correct 56 ms 6112 KB Output is correct
58 Correct 63 ms 6192 KB Output is correct
59 Correct 167 ms 6060 KB Output is correct
60 Correct 61 ms 6464 KB Output is correct
61 Correct 66 ms 6420 KB Output is correct
62 Correct 198 ms 6456 KB Output is correct
63 Correct 140 ms 6396 KB Output is correct
64 Correct 411 ms 6516 KB Output is correct
65 Correct 261 ms 6452 KB Output is correct
66 Correct 212 ms 6420 KB Output is correct
67 Correct 154 ms 6508 KB Output is correct
68 Correct 78 ms 6440 KB Output is correct
69 Correct 95 ms 6452 KB Output is correct
70 Correct 66 ms 6428 KB Output is correct
71 Correct 83 ms 6444 KB Output is correct
72 Incorrect 63 ms 6556 KB Output isn't correct
73 Incorrect 81 ms 6472 KB Output isn't correct
74 Correct 111 ms 6464 KB Output is correct
75 Correct 146 ms 6452 KB Output is correct
76 Correct 106 ms 6464 KB Output is correct
77 Correct 62 ms 6456 KB Output is correct
78 Correct 115 ms 6416 KB Output is correct
79 Correct 97 ms 6440 KB Output is correct
80 Correct 106 ms 6484 KB Output is correct
81 Correct 117 ms 6448 KB Output is correct
82 Correct 112 ms 6464 KB Output is correct
83 Correct 117 ms 6440 KB Output is correct
84 Correct 111 ms 6436 KB Output is correct
85 Correct 147 ms 6492 KB Output is correct
86 Correct 114 ms 6456 KB Output is correct
87 Correct 149 ms 6448 KB Output is correct
88 Correct 122 ms 6436 KB Output is correct
89 Correct 109 ms 6420 KB Output is correct
90 Correct 122 ms 6432 KB Output is correct
91 Correct 152 ms 6460 KB Output is correct
92 Correct 149 ms 6692 KB Output is correct