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Submission #629686

# Submission time Handle Problem Language Result Execution time Memory
629686 2022-08-14T22:03:36 Z 54skyxenon Mecho (IOI09_mecho) C++17
89 / 100
 450 ms 11660 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({make_pair(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 3 ms 5368 KB Output is correct
5 Correct 3 ms 5460 KB Output is correct
6 Correct 3 ms 5460 KB Output is correct
7 Correct 195 ms 11600 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 2 ms 5460 KB Output is correct
12 Correct 3 ms 5460 KB Output is correct
13 Incorrect 3 ms 5460 KB Output isn't correct
14 Correct 4 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 4 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 5460 KB Output is correct
25 Correct 3 ms 5460 KB Output is correct
26 Correct 3 ms 5460 KB Output is correct
27 Correct 3 ms 5432 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 5464 KB Output is correct
32 Correct 4 ms 5460 KB Output is correct
33 Correct 24 ms 6664 KB Output is correct
34 Correct 21 ms 6660 KB Output is correct
35 Correct 37 ms 6660 KB Output is correct
36 Correct 20 ms 6984 KB Output is correct
37 Correct 24 ms 7092 KB Output is correct
38 Correct 51 ms 7000 KB Output is correct
39 Correct 25 ms 7356 KB Output is correct
40 Correct 29 ms 7432 KB Output is correct
41 Correct 69 ms 7408 KB Output is correct
42 Correct 36 ms 8072 KB Output is correct
43 Correct 38 ms 8076 KB Output is correct
44 Correct 81 ms 8028 KB Output is correct
45 Correct 54 ms 8608 KB Output is correct
46 Correct 41 ms 8520 KB Output is correct
47 Correct 108 ms 8500 KB Output is correct
48 Correct 48 ms 9060 KB Output is correct
49 Correct 50 ms 9024 KB Output is correct
50 Correct 95 ms 9008 KB Output is correct
51 Correct 56 ms 9580 KB Output is correct
52 Correct 64 ms 9640 KB Output is correct
53 Correct 167 ms 9500 KB Output is correct
54 Correct 72 ms 10320 KB Output is correct
55 Correct 72 ms 10228 KB Output is correct
56 Correct 188 ms 10156 KB Output is correct
57 Correct 80 ms 10844 KB Output is correct
58 Correct 86 ms 10916 KB Output is correct
59 Correct 213 ms 10932 KB Output is correct
60 Correct 90 ms 11516 KB Output is correct
61 Correct 89 ms 11456 KB Output is correct
62 Correct 221 ms 11544 KB Output is correct
63 Correct 189 ms 11500 KB Output is correct
64 Correct 450 ms 11508 KB Output is correct
65 Correct 304 ms 11584 KB Output is correct
66 Correct 238 ms 11492 KB Output is correct
67 Correct 187 ms 11536 KB Output is correct
68 Correct 95 ms 11544 KB Output is correct
69 Correct 116 ms 11488 KB Output is correct
70 Correct 98 ms 11488 KB Output is correct
71 Correct 99 ms 11480 KB Output is correct
72 Incorrect 87 ms 11548 KB Output isn't correct
73 Incorrect 100 ms 11588 KB Output isn't correct
74 Correct 168 ms 11536 KB Output is correct
75 Correct 197 ms 11520 KB Output is correct
76 Correct 123 ms 11568 KB Output is correct
77 Correct 77 ms 11540 KB Output is correct
78 Correct 135 ms 11600 KB Output is correct
79 Correct 115 ms 11528 KB Output is correct
80 Correct 162 ms 11660 KB Output is correct
81 Correct 152 ms 11636 KB Output is correct
82 Correct 139 ms 11580 KB Output is correct
83 Correct 152 ms 11524 KB Output is correct
84 Correct 137 ms 11552 KB Output is correct
85 Correct 211 ms 11524 KB Output is correct
86 Correct 158 ms 11516 KB Output is correct
87 Correct 166 ms 11524 KB Output is correct
88 Correct 137 ms 11560 KB Output is correct
89 Correct 152 ms 11508 KB Output is correct
90 Correct 184 ms 11512 KB Output is correct
91 Correct 171 ms 11468 KB Output is correct
92 Correct 186 ms 11532 KB Output is correct