[CQOI 2018]社交网络

Description

题库链接

求 \(n\) 个点以 \(1\) 为根的有向生成树个数。

\(1\leq n\leq 250\)

Solution

我终于会 \(\texttt{Matrix-Tree}\) 辣！！

写详解是不可能的，直接丢链接。

注意的是有向图度数矩阵是入度。

Code

#include 
using namespace std;
const int N = 250+5, yzh = 10007;

int n, m, u, v, a[N][N];

int gauss() {
    int ans = 1;
    for (int i = 2; i <= n; i++) {
        for (int j = i+1; j <= n; j++)
            while (a[j][i]) {
                int t = a[i][i]/a[j][i];
                for (int k = i; k <= n; k++) (a[i][k] -= a[j][k]*t%yzh) %= yzh;
                swap(a[i], a[j]); ans *= -1;
            }
        (ans *= a[i][i]) %= yzh;
    }
    return (ans+yzh)%yzh;
}
void work() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= m; i++) {
        scanf("%d%d", &v, &u);
        ++a[v][v], --a[u][v];
    }
    printf("%d\n", gauss());
}
int main() {work(); return 0; }

转载于:https://www.cnblogs.com/NaVi-Awson/p/8984437.html