ural 1627

与论文题没什么区别

#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <map>
#include <stack>
#include <set>
#include <sstream>
#include <fstream>
#include <cmath>
#include <functional>
#include <algorithm>
#include <queue>
#include <cstdlib>
#include <numeric>
#include <bitset>
#include <iomanip>
using namespace std;
typedef long long ll;
#define lson l , m ,rt<<1
#define rson m+1,r,rt<<1|1
typedef vector<string> VS;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<VVI> VVVI;
typedef pair<int, int> pii;
const int mod = 1000000000;
const int N = 511;
const int M = 1111111;
ll det[N][N];
int num[N][N];
char s[N][N];
int dx[] = { 0, 1, 0, -1 };
int dy[] = { 1, 0, -1, 0 };
int n, m;
int cnt;
ll Det(int n) {
	ll ans = 1;
	int i, j, k;
	for (i = 0; i < n; ++i) {
		for (j = i + 1; j < n; ++j) {
			while (det[j][i]) {
				ll t = det[i][i] / det[j][i];
				for (k = i; k < n; ++k) {
					det[i][k] -= det[j][k] * t;
					det[i][k] %= mod;
				}
				for (k = 0; k < n; ++k)
					swap(det[i][k], det[j][k]);
				ans *= -1;
			}
		}
		if (!det[i][i])
			return 0;
	}
	for (i = 0; i < n; ++i)
		ans = ans * det[i][i] % mod;
	return (ans % mod + mod) % mod;
}
int main() {
	int x, y;
	int u, i, k, j;
	scanf("%d%d", &n, &m);
	for (i = 0; i < n; ++i)
		scanf("%s", s[i]);
	for (i = 0; i < n; ++i)
		for (j = 0; j < m; ++j)
			if (s[i][j] == '.')
				num[i][j] = cnt++;
	for (i = 0; i < n; ++i) {
		for (j = 0; j < m; ++j) {
			if (s[i][j] == '*')
				continue;
			u = num[i][j];
			int c = 0;
			for (k = 0; k < 4; ++k) {
				x = i + dx[k];
				y = j + dy[k];
				if (x < 0 || x >= n || y < 0 || y >= m)
					continue;
				if (s[x][y] == '.')
					det[u][num[x][y]] = -1, c++;
			}
			det[u][u] = c;
		}
	}
	printf("%I64d\n", Det(cnt - 1));
	return 0;
}