Submission #943122

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
943122	2024-03-11T08:32:20 Z	tkm_algorithms	Mecho (IOI09_mecho)	C++17	100 / 100	432 ms	7112 KB

mecho

#include <bits/stdc++.h>
using namespace std;


#define ff first
#define ss second
using pi = pair<int, int>;
using vpi = vector<pi>;

const int N = 805;
int n, s, b[N][N], m[N][N];
int dr[] = {0, 0, -1, 1};
int dc[] = {-1, 1, 0, 0};
char a[N][N];  // the grid
pi st;  // the starting position for mecho
vpi h;  // locations of all of the bee hives

bool good(int r, int c){  // is cell (r, c) within bounds?
	return 0 <= r && r < n && 0 <= c && c < n;
}

bool ok(int t){  // can the answer be t?
	memset(b, -1, sizeof b);
	memset(m, -1, sizeof m);
	queue<pi> q;  // all of the current bees' possible locations
	for(auto x: h){
		q.push(x);
		b[x.ff][x.ss] = 0;
	}

	// the bees "expand" for t seconds
	while(!q.empty()){  // bfs
		auto[r, c] = q.front();

		if(b[r][c]==t)
			break;
		q.pop();

		for(int i = 0; i < 4; ++i){
			int r2 = r + dr[i];
			int c2 = c + dc[i];
			if(good(r2, c2)&&(a[r2][c2]=='M'||a[r2][c2]=='G')&&b[r2][c2]==-1){
				b[r2][c2] = b[r][c] + 1;
				q.emplace(r2, c2);
			}
		}
	}

	queue<pi> q2;  // mecho's possible locations
	q2.push(st);
	m[st.ff][st.ss] = 0;
	int t2 = t;
	while(!q2.empty()){
		t2++;

		// mecho's possible locations "expand" for 1 second (where he can take up to s steps)
		while(!q2.empty()){ // bfs
			auto[r, c] = q2.front();
			if(m[r][c]==(t2-t)*s)
				break;
			q2.pop();
			if(~b[r][c])
				continue;
			for(int i = 0; i < 4; ++i){
				int r2 = r + dr[i];
				int c2 = c + dc[i];
				if(good(r2, c2)&&b[r2][c2]==-1&&m[r2][c2]==-1&&
						(a[r2][c2]=='G'||a[r2][c2]=='D')){
					if(a[r2][c2]=='D')  // did mecho just find home??
						return true;  // success!
					m[r2][c2] = m[r][c] + 1;
					q2.emplace(r2, c2);
				}
			}
		}

		// the bees' possible locations "expand" by 1 second
		while(!q.empty()){  // bfs
			auto[r, c] = q.front();

			if(b[r][c]==t2)
				break;
			q.pop();
			for(int i = 0; i < 4; ++i){
				int r2 = r + dr[i];
				int c2 = c + dc[i];

				if(good(r2, c2)&&b[r2][c2]==-1&&(a[r2][c2]=='G'||a[r2][c2]=='M')){
					b[r2][c2] = b[r][c] + 1;
					q.emplace(r2, c2);
				}
			}
		}
	}
	return false;  // mecho never found home without encountering bees :(
}

int main() {
	ios::sync_with_stdio(0); cin.tie(0);

	cin >> n >> s;
	for(int i = 0; i < n; ++i)
		for(int j = 0; j < n; ++j){
			cin >> a[i][j];
			if(a[i][j]=='M')
				st = {i, j};
			else if(a[i][j]=='H')
				h.emplace_back(i, j);
		}

	// binary search (yes this binary search might not be commonly seen, but it's shorter to write)
	int ans = -1;
	for(int u = int(1e6); u > 0; u /= 2)
		while(ans + u <= int(1e6) && ok(ans + u))
			ans += u;
	cout << ans;
}

Subtask #1

100.0 / 100.0

#	Verdict	Execution time	Memory	Grader output
1	Correct	3 ms	5980 KB	Output is correct
2	Correct	4 ms	5976 KB	Output is correct
3	Correct	4 ms	5980 KB	Output is correct
4	Correct	3 ms	5980 KB	Output is correct
5	Correct	3 ms	5980 KB	Output is correct
6	Correct	4 ms	5980 KB	Output is correct
7	Correct	305 ms	6316 KB	Output is correct
8	Correct	3 ms	5980 KB	Output is correct
9	Correct	3 ms	5980 KB	Output is correct
10	Correct	4 ms	5980 KB	Output is correct
11	Correct	4 ms	5980 KB	Output is correct
12	Correct	4 ms	5980 KB	Output is correct
13	Correct	4 ms	6048 KB	Output is correct
14	Correct	4 ms	5980 KB	Output is correct
15	Correct	4 ms	5980 KB	Output is correct
16	Correct	3 ms	5980 KB	Output is correct
17	Correct	4 ms	5980 KB	Output is correct
18	Correct	3 ms	5980 KB	Output is correct
19	Correct	4 ms	5980 KB	Output is correct
20	Correct	4 ms	5980 KB	Output is correct
21	Correct	4 ms	5980 KB	Output is correct
22	Correct	4 ms	5976 KB	Output is correct
23	Correct	4 ms	5876 KB	Output is correct
24	Correct	4 ms	5980 KB	Output is correct
25	Correct	4 ms	5980 KB	Output is correct
26	Correct	5 ms	5980 KB	Output is correct
27	Correct	6 ms	5980 KB	Output is correct
28	Correct	4 ms	6008 KB	Output is correct
29	Correct	6 ms	5980 KB	Output is correct
30	Correct	5 ms	6056 KB	Output is correct
31	Correct	6 ms	5976 KB	Output is correct
32	Correct	5 ms	5980 KB	Output is correct
33	Correct	31 ms	6248 KB	Output is correct
34	Correct	30 ms	6236 KB	Output is correct
35	Correct	37 ms	6236 KB	Output is correct
36	Correct	38 ms	6236 KB	Output is correct
37	Correct	34 ms	6236 KB	Output is correct
38	Correct	51 ms	6240 KB	Output is correct
39	Correct	49 ms	6236 KB	Output is correct
40	Correct	45 ms	6236 KB	Output is correct
41	Correct	75 ms	6220 KB	Output is correct
42	Correct	68 ms	6312 KB	Output is correct
43	Correct	64 ms	6236 KB	Output is correct
44	Correct	78 ms	6232 KB	Output is correct
45	Correct	62 ms	6232 KB	Output is correct
46	Correct	68 ms	6344 KB	Output is correct
47	Correct	93 ms	6232 KB	Output is correct
48	Correct	86 ms	6236 KB	Output is correct
49	Correct	88 ms	6364 KB	Output is correct
50	Correct	103 ms	6236 KB	Output is correct
51	Correct	108 ms	6232 KB	Output is correct
52	Correct	94 ms	6404 KB	Output is correct
53	Correct	124 ms	6488 KB	Output is correct
54	Correct	118 ms	6232 KB	Output is correct
55	Correct	114 ms	6488 KB	Output is correct
56	Correct	148 ms	6480 KB	Output is correct
57	Correct	123 ms	6224 KB	Output is correct
58	Correct	142 ms	6508 KB	Output is correct
59	Correct	164 ms	6512 KB	Output is correct
60	Correct	131 ms	6488 KB	Output is correct
61	Correct	132 ms	6552 KB	Output is correct
62	Correct	206 ms	6568 KB	Output is correct
63	Correct	293 ms	6548 KB	Output is correct
64	Correct	301 ms	6524 KB	Output is correct
65	Correct	286 ms	6584 KB	Output is correct
66	Correct	403 ms	6416 KB	Output is correct
67	Correct	266 ms	6564 KB	Output is correct
68	Correct	334 ms	6672 KB	Output is correct
69	Correct	275 ms	6560 KB	Output is correct
70	Correct	292 ms	6608 KB	Output is correct
71	Correct	306 ms	6624 KB	Output is correct
72	Correct	432 ms	6604 KB	Output is correct
73	Correct	270 ms	6864 KB	Output is correct
74	Correct	363 ms	7112 KB	Output is correct
75	Correct	351 ms	6904 KB	Output is correct
76	Correct	352 ms	6836 KB	Output is correct
77	Correct	368 ms	6880 KB	Output is correct
78	Correct	280 ms	6820 KB	Output is correct
79	Correct	317 ms	6740 KB	Output is correct
80	Correct	353 ms	6780 KB	Output is correct
81	Correct	311 ms	6788 KB	Output is correct
82	Correct	275 ms	6800 KB	Output is correct
83	Correct	276 ms	6796 KB	Output is correct
84	Correct	332 ms	6624 KB	Output is correct
85	Correct	333 ms	6736 KB	Output is correct
86	Correct	343 ms	6816 KB	Output is correct
87	Correct	333 ms	6632 KB	Output is correct
88	Correct	306 ms	6752 KB	Output is correct
89	Correct	315 ms	6708 KB	Output is correct
90	Correct	338 ms	6748 KB	Output is correct
91	Correct	332 ms	6744 KB	Output is correct
92	Correct	342 ms	6756 KB	Output is correct