lightoj1034 Hit the Light Switches

思路：开始想的就是普通的dfs就好了，但是样例再次神奇的过了，然后wa成傻逼了。

里面主要是有个贪心的思想，从最高的topo序开始dfs，，，，涨知识了。

// #pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <sstream>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <limits.h>
// #define DEBUG
#ifdef DEBUG
#define debug(...) printf( __VA_ARGS__ )
#else
#define debug(...)
#endif
#define MEM(x,y) memset(x, y,sizeof x)
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> ii;
const int inf = 1 << 30;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const int maxn = 10010;
int head[maxn], nxt[maxn << 4], to[maxn << 4];
int n, m;
bool vis[maxn];
vector<int> topo;
void dfs(int u){
	vis[u] = true;
	for (int i = head[u]; i != -1;i = nxt[i]){
		if (vis[to[i]]) continue;
		dfs(to[i]);
	}
	topo.push_back(u);
}
int tol;
void add(int u,int v){
	to[tol] = v;
	nxt[tol] = head[u];
	head[u] = tol++;
}
int main()
{	
	// freopen("in.txt","r",stdin);
	// freopen("out.txt","w",stdout);
	int t, icase = 0;
	cin >> t;
	while(t--){
		scanf("%d%d",&n,&m);
		MEM(vis, false);
		MEM(head, -1);
		tol = 0;
		int a,b;
		for (int i = 0;i < m;++i){
			scanf("%d%d",&a,&b);
			add(a,b);
		}
		topo.clear();
		for (int i = 1;i <= n;++i)
			if (!vis[i]) dfs(i);
		// for (int i = 0;i < n;++i){
		// 	printf("%d\t", topo[i]);
		// }
		// printf("\n\n"); 
		int cnt = 0;
		MEM(vis, false);
		for (int i = n - 1;i >= 0;--i){
			int u = topo[i];
			if (vis[u]) continue;
			dfs(u);
			cnt++;
		}
		printf("Case %d: %d\n", ++icase, cnt);
	}
	return 0;
}