uva 11174

本文主要是介绍uva 11174，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

刘书上例题  

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <sstream>
#include <string>
#include <cstring>
#include <algorithm>
#include <iostream>
#define maxn 40010
#define INF 0x7fffffff
#define inf 10000000
#define MOD 1000000007
#define ull unsigned long long
#define ll long long
using namespace std;ll fac[maxn];
int c[maxn];
bool vis[maxn];
vector<int> g[maxn];void init()
{fac[1] = 1;for(int i = 2; i < maxn; ++ i) fac[i] = fac[i-1]*i%MOD;
}ll pow_mod(ll a, ll p, ll n)
{if(p == 0) return 1;ll ans = pow_mod(a, p/2, n);ans = ans*ans%n;if(p%2) ans = ans*a%n;return ans;
}void dfs(int u)
{c[u] = 1;vis[u] = true;for(int i = 0; i < (int)g[u].size(); ++ i){if(!vis[g[u][i]]) dfs(g[u][i]);c[u] += c[g[u][i]];}
}int main()
{int t, m, n;scanf("%d", &t);init();while(t --){memset(vis, 0, sizeof(vis));scanf("%d%d", &n, &m);for(int i = 1; i <= n; ++ i) g[i].clear();for(int i = 0; i < m; ++ i){int u, v;scanf("%d%d", &u, &v);g[v].push_back(u);}for(int i = 1; i <= n; ++ i)if(!vis[i]) dfs(i);long long ans = fac[n];for(int i = 1; i <= n; ++ i){long long k = pow_mod(c[i], MOD - 2, MOD);ans = ans * k % MOD;}printf("%lld\n", ans);}return 0;
}

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