Lightoj-1034-tarjan

The main topic: There are n lights, need to light them all, then there is M-line U,v said U Lit, V is also lit, asked at least a few lights to light;

Problem Analysis: Tarjan first to find all the strong connectivity components, Map[i] that the first point in the first few strong connected components, and then we need DFS each strong connected component, if found Map[u]!=map[v], that is, two strong connected components have an edge between, So that one side can be shed, because we can always in the map[u] in the component of the other component to reach any edge;

AC Code:

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<string>
#include<vector>
#include<stack>
using namespace std;
const int MAX=10010;
vector<int>vec[MAX];
int map[MAX],dfn[MAX],low[MAX],tot[MAX],depth,scc,ans,n,m;
stack<int>s;
void init()
{
	int i;
	depth=scc=ans=0;
	for(i=0;i<MAX;i++)
		vec[i].clear();
	memset(map,-1,sizeof(map));
	memset(tot,0,sizeof(tot));
	memset(low,0,sizeof(low));
	memset(dfn,-1,sizeof(dfn));
}
void tarjan(int u)
{
	int i;
	dfn[u]=low[u]=depth++;
	s.push(u);
	for(i=0;i<vec[u].size();i++)
	{
		int v=vec[u][i];
		if(dfn[v]==-1)
		{
			tarjan(v);
			low[u]=min(low[u],low[v]);
		}
		else if(map[v]==-1)
			low[u]=min(low[u],dfn[v]);
	}
	if(low[u]==dfn[u])
	{
		int v;
		do{  
           v = s.top();  
           map[v] = scc;  
           s.pop();  
        }while(v!=u);  
        scc++;  
	}
}
void dfs(int u)
{
	int i,v;
	dfn[u]=1;
	for(i=0;i<vec[u].size();i++)
	{
		v=vec[u][i];
		if(map[u]!=map[v])	tot[map[v]]++;
		if(!dfn[v])	dfs(v);
	}
}
int main()
{
	int cas,c,i,u,v;
	scanf("%d",&cas);
	for(c=1;c<=cas;c++)
	{
		init();
		scanf("%d%d",&n,&m);
		for(i=0;i<m;i++)
		{
			scanf("%d%d",&u,&v);
			u--;
			v--;
			vec[u].push_back(v);
		}
		for(i=0;i<n;i++)
			if(dfn[i]==-1)
				tarjan(i);
		memset(dfn,0,sizeof(dfn));
		for(i=0;i<n;i++)
			if(!dfn[i])
				dfs(i);
		for(i=0;i<scc;i++)
		{
			if(!tot[i])
				ans++;
		}
		printf("Case %d: %d\n",c,ans);
	}		
	return 0;
}