Submission #258861

#	Time	Username	Problem	Language	Result	Execution time	Memory
258861		c4ts0up	Mecho (IOI09_mecho)	C++17	100 / 100	277 ms	5024 KiB

mecho

/*
ID: c4ts0up
LANG: C++
TASK: Mecho
*/

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define pb push_back
#define ff first
#define ss second

const int NMAX = 805;
const int INF = 1e9;

int n, s;
pair <int,int> home, mecho;
char grid[NMAX][NMAX];
int dist[NMAX][NMAX];
bool seen[NMAX][NMAX];

// hace el check a una coordenada
bool Check(int row, int col) {
	return (0 <= row && row < n && 0 <= col && col < n);
}

// BFS para encontrar el tiempo requerido para que las abejas lleguen a un lugar
void EncontrarDistancias() {
	queue <pair <int,int> > to;
	
	for (int i=0; i<=n; i++) for (int j=0; j<=n; j++) seen[i][j] = false;
	
	for (int i=0; i<n; i++) for (int j=0; j<n; j++) {
		if (grid[i][j] == 'H') to.push({i,j}), dist[i][j] = 0;
		else dist[i][j] = INF;
	}

	while (!to.empty()) {
		pair <int,int> curr = to.front();
		to.pop();
		
		// ya lo visitamos
		if (seen[curr.ff][curr.ss]) continue;
		
		if (grid[curr.ff][curr.ss] == 'T' || grid[curr.ff][curr.ss] == 'D') {
			seen[curr.ff][curr.ss] = true;
			continue;
		}
		
		// visitamos a todos los vecinos
		if (Check(curr.ff+1, curr.ss) && dist[curr.ff+1][curr.ss] > dist[curr.ff][curr.ss]+1) to.push({curr.ff+1, curr.ss}), dist[curr.ff+1][curr.ss] = dist[curr.ff][curr.ss]+1;
		if (Check(curr.ff-1, curr.ss) && dist[curr.ff-1][curr.ss] > dist[curr.ff][curr.ss]+1) to.push({curr.ff-1, curr.ss}), dist[curr.ff-1][curr.ss] = dist[curr.ff][curr.ss]+1;
		if (Check(curr.ff, curr.ss+1) && dist[curr.ff][curr.ss+1] > dist[curr.ff][curr.ss]+1) to.push({curr.ff, curr.ss+1}), dist[curr.ff][curr.ss+1] = dist[curr.ff][curr.ss]+1;
		if (Check(curr.ff, curr.ss-1) && dist[curr.ff][curr.ss-1] > dist[curr.ff][curr.ss]+1) to.push({curr.ff, curr.ss-1}), dist[curr.ff][curr.ss-1] = dist[curr.ff][curr.ss]+1;
		
		seen[curr.ff][curr.ss] = true;
	}
}

bool BFS(int minutos) {
	queue <pair <int, pair <int,int> > > to;
	to.push({0, mecho});
	
	for (int i=0; i<=n; i++) for (int j=0; j<=n; j++) seen[i][j] = false;
	
	while (!to.empty()) {
		pair <int, pair <int,int> > curr = to.front();
		to.pop();
		
		int r = curr.ss.ff;
		int c = curr.ss.ss;
		int pasos = curr.ff;
		
		//cerr << "Visitando <" << r << ", " << c << "> luego de " << pasos << " pasos (pasos/s = " << (max(pasos, 0)/s) << ")" << endl;
		
		// ya lo visitamos, no tenemos que volver
		if (seen[r][c]) continue;
		
		// no podemos atravesarlo
		if (grid[r][c] == 'T') {
			seen[r][c] = true;
			continue;
		}
		else if (grid[r][c] == 'D') return true;
		
		// ya está infestado de abejas, o sea, bloqueado
		if (minutos + (max(pasos, 0)/s) >= dist[r][c]) {
			seen[r][c] = true;
			continue;
		}
		
		// visitamos a todos los vecinos
		
		
		if (!seen[r+1][c] && Check(r+1, c)) to.push({pasos+1, {r+1,c}});
		if (!seen[r-1][c] && Check(r-1, c)) to.push({pasos+1, {r-1,c}});
		if (!seen[r][c+1] && Check(r, c+1)) to.push({pasos+1, {r,c+1}});
		if (!seen[r][c-1] && Check(r, c-1)) to.push({pasos+1, {r,c-1}});
		
		seen[r][c] = true;
	}
	
	return false;
}


int main() {
	/*//
	freopen("test.in", "r", stdin);
	freopen("", "w", stdout);
	//*/
	
	cin >> n >> s;
	for (int i=0; i<n; i++) {
		string aux;
		cin >> aux;
		for (int j=0; j<n; j++) {
			grid[i][j] = aux[j];
			
			if (grid[i][j] == 'M') mecho = {i,j};
			else if (grid[i][j] == 'D') home = {i,j};
		}
		
		
	}
	
	EncontrarDistancias();
	
	/*//
	for (int i=0; i<n; i++) {
		for (int j=0; j<n; j++) {
			if (grid[i][j] == 'T' || grid[i][j] == 'D') cerr << grid[i][j] << " ";
			else cerr << dist[i][j] << " ";
		}
		cerr << endl;
	}
	//*/
	
	if (!BFS(0)) {
		cout << -1 << endl;
		exit(0);
	}
	
	int lb = 0, ub = 1e6, mid;
	while (lb <= ub) {
		mid = (lb+ub)/2;
		
		//cerr << "--- mid = " << mid << endl;
		if (BFS(mid)) lb = mid+1;
		else ub = mid-1;
	}
	
	//cerr << "lb = " << lb << "; ub = " << ub << "; mid = " << mid << endl;
	cout << ub << endl;
	return 0;
}

• Subtask 1: 100 / 100