Submission #767661

#	Time	Username	Problem	Language	Result	Execution time	Memory
767661		lukehsiao	Tracks in the Snow (BOI13_tracks)	C++14	5.52 / 100	1398 ms	1048576 KiB

tracks

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

const int mxN = 4000;

int H, W, id[mxN][mxN];
char grid[mxN][mxN];
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};

vector<set<int>> adj;
vector<int> dist;

void ff(int r, int c, int x) {
	id[r][c] = x;
	
	for (int i=0; i<4; ++i) {
		int nr = r + dx[i], nc = c + dy[i];
		if (nr >= 0 && nr < H && nc >= 0 && nc < W &&
				grid[nr][nc] == grid[r][c] && !id[nr][nc]) {
			ff(nr, nc, x);
		}
	}
}

void ff2(int r, int c, int x) {
	id[r][c] = 0;

	for (int i=0; i<4; ++i) {
		int nr = r + dx[i], nc = c + dy[i];
		if (nr >= 0 && nr < H && nc >= 0 && nc < W && id[nr][nc]) {
			if (id[nr][nc] != x)
				adj[x-1].insert(id[nr][nc]-1);
			else
				ff2(nr, nc, x);
		}
	}
}

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

	cin >> H >> W;
	for (int i=0; i<H; ++i)
		for (int j=0; j<W; ++j)
			cin >> grid[i][j];
	
	int cur = 0;
	for (int i=0; i<H; ++i) {
		for (int j=0; j<W; ++j) {
			if (!id[i][j] && grid[i][j] != '.')
				ff(i, j, ++cur);
		}
	}

	adj.resize(cur);
	dist.resize(cur, 2e9);

	for (int i=0; i<H; ++i) {
		for (int j=0; j<W; ++j) {
			if (id[i][j]) {
				ff2(i, j, id[i][j]);
			}
		}
	}

	queue<int> q;
	q.push(0);
	dist[0] = 0;

	while (!q.empty()) {
		int x = q.front();
		q.pop();
		for (int u : adj[x]) {
			if (dist[u] == 2e9) {
				dist[u] = dist[x] + 1;
				q.push(u);
			}
		}
	}

	int ans = 0;
	for (int i : dist)
		ans = max(ans, i);
	
	cout << ans + 1 << '\n';
}

• Subtask 1: 3.3333333333333335 / 30
• Subtask 2: 2.1875 / 70