UVa LA 4287 强连通 （类似 hdu 3836）

#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn = 20009;
const int maxm = 50009;

struct node
{
	int v,next;
}eg[maxm];
int head[maxn],in[maxn],out[maxn],belong[maxn];
int insta[maxn],dfn[maxn] ,low[maxn],sta[maxn];
int tot,Index,top,color,n;

inline int min(int a,int b){return a < b ? a : b;}
inline int max(int a,int b){return a > b ? a : b;}

inline void add(int a,int b)
{
	eg[tot].v = b;
	eg[tot].next = head[a];
	head[a] = tot++;
}
void init()
{
	memset(low,0,sizeof(low));
	memset(dfn,0,sizeof(dfn));
	memset(sta,0,sizeof(sta));
	memset(head,-1,sizeof(head));
	memset(belong,0,sizeof(belong));
	memset(in,0,sizeof(in));
	memset(out,0,sizeof(out));
	tot = Index = top = color = 0;
}
void tarjan(int u)
{
	dfn[u] = low[u] = ++Index;
	sta[top++] = u;
	insta[u] = 1;
	for(int i = head[u];i+1;i=eg[i].next)
	{
		int v= eg[i].v;
		if(!dfn[v])
		{
			tarjan(v);
			low[u] = min(low[u],low[v]);
		}else if(insta[v])
		{
			low[u] = min(low[u],dfn[v]);
		}
	}
	if(low[u] == dfn[u])
	{
		int v;
		color ++;  //强连通个数
		do
		{
			v = sta[--top];
			insta[v] = 0;
			belong[v] = color;
		}while(u != v);
	}
}
void buildtree()
{
	for(int u=1;u<=n;u++)
	{
		for(int i = head[u];i+1;i=eg[i].next)
		{
			int v = eg[i].v;
			if(belong[u] != belong[v]) //缩点
			{
				out[belong[u]] ++;
				in[belong[v]] ++;
			}
		}
	}
}
void work()
{
	int i,a=0,b=0;
	for(i = 1;i<=n;i++)
		if(!dfn[i]) tarjan(i);
		buildtree();
		for(i=1;i<=color;i++) 
		{
			if(in[i] == 0) a++; //入度为零的点
			if(out[i] == 0) b++; //出度为零的点
		}
		if(color == 1) //图本身是强连通的就不需要
			printf("0\n");
		else
			printf("%d\n",max(a,b));
}
int main()
{
	int a,b,m,i;
	int t;
	scanf("%d",&t);
	while(t--)
	{
		init();
		scanf("%d%d",&n,&m);
		for(i=0;i<m;i++)
		{
			scanf("%d%d",&a,&b);
			add(a,b);
		}
		work();
	}
	return 0;
}

/*

2
3 2
1 2
1 3
3 2
1 2
1 3


  */