线性代数

int sol(void) {
    int f = 1;
    for (int i = 1; i <= n; ++i)
        for (int j = i + 1; j <= n; ++j) {
            while (a[i][i]) {
                int d = a[j][i] / a[i][i];
                for (int k = i; k <= n; ++k)
                    a[j][k] = (a[j][k] - 1ll * d * a[i][k] % P + P) % P;
                swap(a[i], a[j]), f = -f;
            }
            swap(a[i], a[j]); f = -f;
        }
    int ans = f;
    for (int i = 1; i <= n; ++i) ans = 1ll * ans * a[i][i] % P;
    return (ans + P) % P;
}