tarjan.cpp

/*
 * Tarjan算法
 * 复杂度O(N+M)
 */
const int MAXN = 20010;//点数
const int MAXM = 50010;//边数
struct Edge
{
	int to,next;
}edge[MAXM];
int head[MAXN],tot;
int Low[MAXN],DFN[MAXN],Stack[MAXN],Belong[MAXN];//Belong数组的值是1~scc
int Index,top;
int scc;//强连通分量的个数
bool Instack[MAXN];
int num[MAXN];//各个强连通分量包含点的个数，数组编号1~scc
//num数组不一定需要，结合实际情况
void addedge(int u,int v)
{
	edge[tot].to = v;edge[tot].next = head[u];head[u] = tot++;
}
void Tarjan(int u)
{
	int v;
	Low[u] = DFN[u] = ++Index;
	Stack[top++] = u;
	Instack[u] = true;
	for(int i = head[u];i != -1;i = edge[i].next)
	{
		v = edge[i].to;
		if( !DFN[v] )
		{
			Tarjan(v);
			if( Low[u] > Low[v] )Low[u] = Low[v];
		}
		else if(Instack[v] && Low[u] > DFN[v])
			Low[u] = DFN[v];
	}
	if(Low[u] == DFN[u])
	{
		scc++;
		do
		{
			v = Stack[--top];
			Instack[v] = false;
			Belong[v] = scc;
			num[scc]++;
		}
		while( v != u);
	}
}
void solve(int N)
{
	memset(DFN,0,sizeof(DFN));
	memset(Instack,false,sizeof(Instack));
	memset(num,0,sizeof(num));
	Index = scc = top = 0;
	for(int i = 1;i <= N;i++)
		if(!DFN[i])
			Tarjan(i);
}
void init()
{
	tot = 0;
	memset(head,-1,sizeof(head));
}